(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Bulletin of the Natural History Museum Zoology"

ISSN 0968-0470 



Bulletin of 
The Natural History 
Museum _ 



Zoology Series 




THE 

NATURAL 
HISTORY 
MUSEUM 



VOLUME 61 NUMBER 1 29 JUNE 1995 



The Bulletin of The Natural History Museum (formerly: Bulletin of the British Museum 
(Natural History)), instituted in 1949, is issued in four scientific series, Botany, 
Entomology, Geology (incorporating Mineralogy) and Zoology. 

The Zoology Series is edited in the Museum's Department of Zoology 
Keeper of Zoology: Dr C.R. Curds 

Editor of Bulletin: Dr N.R. Merrett 

Assistant Editor: Dr B.T. Clarke 



Papers in the Bulletin are primarily the results of research carried out on the unique and ever- 
growing collections of the Museum, both by the scientific staff and by specialists from elsewhere 
who make use of the Museum's resources. Many of the papers are works of reference that will 
remain indispensable for years to come. All papers submitted for publication are subjected to 
external peer review for acceptance. 

A volume contains about 160 pages, made up by two numbers, published in the Spring and Autumn. 
Subscriptions may be placed for one or more of the series on an annual basis. Individual numbers 
and back numbers can be purchased and a Bulletin catalogue, by series, is available. Orders and 
enquiries should be sent to: 

Intercept Ltd. 
P.O. Box 716 
Andover 
Hampshire SP10 1YG 

Telephone: (01264) 334748 
Fax: (01264) 334058 

Claims for non-receipt of issues of the Bulletin will be met free of charge if received by the Publisher 
within 6 months for the UK, and 9 months for the rest of the world. 



World List abbreviation: Bull. nat. Hist. Mus. Lond. (Zool.) 
© The Natural History Museum, 1995 



Zoology Series 
ISSN 0968 - 0470 Vol. 61, No. 1, pp. 1-90 

The Natural History Museum 

Cromwell Road 

London SW7 5BD Issued 29 June 1995 

Typeset by Ann Buchan (Typesetters), Middlesex 
Printed in Great Britain at The Alden Press, Oxford 



Bull. nat. Hist. Mus. Lond. (Zool.) 61(1): 1-10 



Issued 29 June 1995 



A revised familial classification for certain 
cirrhitoid genera (Teleostei, Percoidei 
Cirrhitoidea), with comments on the group 
monophyly and taxonomic ranking 



S THE NATURAL 
HISTORY MU^EL 

-7 JUL 1995 



P.H. GREENWOOD 1 



Honorary Research Associate, J.L.B. Smith Institute of Ichthyology, Private Bag 1015, GraharrtSTtn 
6140, South Africa and Visiting Research Fellow, The Natural History Museum, Cromwell Road, 
London SW7 5 BD 



PHt:obivic:D 
ZOOLOGY LIBRA 



CONTENTS 



Introduction 1 

Methods and materials 2 

Urohyal morphology and the suprageneric classification of the cirrhitoid fishes, particularly the genus 

Acantholatris and species currently referred to the genus Nemadactylus 2 

The familial classification of Acantholatris Gill, 1862, and Nemadactylus Richardson, 1839 5 

Possible lineages within the Latridae as now expanded to include the genera Acantholatris and 

Nemadactylus 5 

Taxonomic and phylogenetic conclusions 6 

Taxonomy 6 

The cirrhitoids as a monophyletic lineage 6 

Intragroup relationships within the cirrhitoids 8 

Acknowledgements 9 

References 10 



Synopsis. Previous suprageneric classifications of cirrhitoid fishes were based mainly on superficial characters. 
Recent anatomical studies show that five morphologically distinct types of urohyal bone occur within the group, and 
that on this basis certain taxa have been misplaced at both the generic and familial levels. The monophyly of the 
cirrhitoid fishes, tacitly assumed by previous authors, is reviewed, and an hypothesis of their monophyly erected on 
the basis of several synapomorphic features. It is also proposed, on the basis of those synapomorphies, that the 
lineage be given subordinal rank within the Perciformes. 



INTRODUCTION 



During an investigation into the cranial and branchial muscles 
associated with feeding in certain cirrhitoid fishes from South 
African waters, it became apparent that five distinct morpho- 
types of urohyal occur within the group. Two very distinct 
types are found in genera currently classified as members of 
the Cheilodactylidae; of these two forms, one also occurs in 
genera referred to the family Latridae by Regan. Despite the 
passage of over 80 years since Regan's (1911) paper was 
published, it remains the most recent suprageneric classifica- 
tion of these fishes, which he arranged in five families, viz 
Cirrhitidae, Cheilodactylidae, Aplodactylidae, Chironemidae 
and Latridae, grouping them informally as the 'cirrhitiform 
percoids'. 

Like its predecessor, namely Gill's more detailed paper of 
1862, Regan's later analysis was based mainly on external 

t Dr Greenwood died 3 March 1995. 
©The Natural History Museum, 1995 



features. Apart from some comments by Regan on cranial 
features, vertebral numbers and vertebral morphology, nei- 
ther paper included any other anatomical information on 
these fishes. 

Although Regan (1911) expressed some doubts about the 
familial status given by him to the five generic assemblages he 
recognised (suggesting that subfamilial rank could be more 
appropriate) he did not comment on Gill's (1862) earlier 
classfication which recognised four subfamilies within a single 
family, the Cirrhitoidae; indeed, and inexplicably, Regan 
{op. cit.) makes no reference at all to Gill's paper. 

Gill's (op. cit) four subfamilies correspond, almost entirely, 
to Regan's families, except that Gill's Latridinae included 
two genera, Nemadactylus Richardson, 1839, and Cheilodac- 
tylus Lacepede, 1803, which Regan incorporated in his family 
Cheilodactylidae; Gill's list of included taxa in his concept of 
the Latridinae also contained two genera not mentioned by 
Regan, despite their being recognised at that time and still 
being recognised today (viz Latridopsis Gill, 1862, and Acan- 
tholatris Gill, 1862). 



PH. GREENWOOD 



The present contribution, it is hoped, will play some part in 
rewakening an interest in a phylogenetically based taxonomy 
of Regan's 'cirrhitiform percoids', and of their interrelation- 
ships within, or perhaps outside, the Percoidei. Regan (1911) 
gave no formal suprafamilial ranking to his 'cirrhitiforms' , 
but in some recent classifications (Nelson, 1994) the group 
has been raised to a superfamily, the Cirrhitoidea. The use of 
the terms 'cirrhitoid' and 'cirrhitoids' in this paper is thus to 
be interpreted as a reference to the superfamily and not to the 
suborder suggested for these fishes on p. 9. 



METHODS AND MATERIALS 

Species of the percoid families Serranidae and Centropomi- 
dae served as outgroup representatives of basal members of 
the Percoidei. The condition and composition of the sterno- 
hyoideus muscles, and the morphology of the urohyal in these 
taxa were taken to represent the plesiomorphic percoid 
conditions. 

Wherever possible, dry skeletal preparations and alizarin 
transparencies were examined, as were radiographs and 
dissections of preserved specimens. 

Study material. The symbols used in the following list are: 
D. Sternohyoid muscle dissected and the urohyal removed or 
examined in situ; X. Radiographed; S. Dry skeletal material 
examined; an asterisk following a binomen indicates that this 
name appears on the box housing the skeleton, and that its 
specific identity could not be checked on the basis of the 
characters preserved. 

The familial grouping used in the list is that resulting from 
the conclusions reached in this paper, and thus differs in some 
respects from the classifications of Gill (1862) and Regan 
(1911), and in some cases that of later authors (see p. 5 
relating to the species 'bergi" and 'gayi previously placed in 
the genus Cheilodactylus and in the family Cheilodactylidae). 

Institutional abbreviations are: BMNH, The Natural His- 
tory Museum, London; DIFS, The Department of Ichthyol- 
ogy and Fisheries Science, Rhodes University, South Africa; 
RUSI, J.L.B. Smith Institute of Ichthyology, South Africa; 
SAM, South African Museum, Cape Town. 

Study material. 
(i) Outgroups. 

Centropomidae; Glaucosomatidae; Ambassidae: The osteo- 
logical and other material listed in Greenwood (1976). 

Serranidae: as above, together with Epinephalus alexandri- 
nus BMNH 1867.2.1: 69-72; (D). 

(ii) Cirrhitoid fishes. 

Aplodactylidae: Aplodactylus punctatus * (type species of 

the genus): BMNH 1873.4.3: 157 (S). 

A. lophodon: BMNH 1914.8.20: 214 (D). 
Cheilodactylidae: Cheilodactylus fasciatus (type species of 

the genus): 3 specimens, DIFS unregistered (D). 

C. fuscus: 1 specimen, DIFS unregistered (D). 

C. pixi: 6 specimens, DIFS unregistered (D). 

2 specimens, DIFS unregistered (S). 

4 'paperfish' larvae, 44-50 mm standard length, 

RUSI 19842 (D). 

1 'paperfish' larva, 44 mm standard length, RUSI 

19842 (S). 

C. zonatus: BMNH 1907.12.23: 238 (S). 



Chirodactylus brachydactylus: 3 specimens, DIFS 

unregistered (D). 

2 specimens, DIFS unregistered (S). 

2 'paperfish' larvae, 33 & 38 mm standard length. 

RUSI, unregistered (D). 

C. grandis: 1 'paperfish' larva, 57 mm standard 

length. RUSI 18404 (D). 

Dactylophora nigricans*: BMNH 1869.2.24:8 (S). 
Chironemidae: Chironemus marmoratus*: BMNH 

1871.3.29: 28 (S). 

Chironemus marmoratus: BMNH 1861.11.7: 6 (D). 
Cirrhitidae: Amblycirrhitus pinos: 2 alizarin preparations 

ex BMNH 1976.7.14: 453-7 (S). 

Amblycirrhitus pinos: BMNH 1984.7.16: 96 (D). 

Cirrhitus maculatus*: BMNH unregistered (S). 

Cirrhitichthys oxycephalus: RUSI 11658; BMNH 

1929.9.20: 8 (D). 

Cirrhitichthys oxycephalus: BMNH 1908.3.23: 77-79 

(X). 

Cyprinocirrhites polyactis: RUSI 12339 (D). 

Gymnocirrhites arcatus (type species of the 

genus):BMNH 1965.12.20: 10 (D). 

Gymnocirrhites arcatus*: BMNH unregistered, col- 
lected by Richardson (S). 

Gymnocirrhites arcatus: BMNH 1865.3.2: 82-83 (X). 

Oxycirrhites typus (type species of the genus): 

BMNH 1929.6.12: 2(D). 

Paracirrhites forsteri: BMNH 1852.9.13: 119 (S) 

Paracirrhites forsteri: BMNH 1969.7.16: 28-32; one 

specimen(D). 
Latridae: Acantholatris bergi BMNH 1936.18.26: 439 (D) 

&(X). 

Acantholatris gayi: BMNH 1879.5.14: 278; 

1890.2.26: 49 (D) & (X). 

Acantholatris monodactylus (type species of the 

genus): BMNH 1960.1.8: 6-13; one (D), all (X). 

Acantholatris monodactylus: BMNH unregistered, 

ex Gough Isl.; 2 specimens, both (S). 

Acantholatris monodactylus: RUSI 33484; 33485; 

33624 (D). 

Latridopsis ciliaris (type species of the genus): 

BMNH 1872.7.1: 32 (S). 

Latridopsis ciliaris: BMNH 1873.12.13: 55 (D) & 

(X). 

Latris lineata: BMNH 1855.9.19: 124 (D). 

Latris lineata: SAM 22623 (D). 

Mendosoma lineatum (type species of the genus): 

BMNH 1960.1.8: 14-21; one (D), all (X). 

Mendosoma lineatum: RUSI 33613; 33625 (D). 

Nemadactylus macropterus: BMNH 1855.9.19: 314 

(X). 

Nemadactylus macropterus: BMNH 1872.7.1: 21 

(D)&(X). 



Urohyal morphology and the suprageneric 
classification of cirrhitoid fishes, particularly the 
genus Acantholatris and species currently referred 
to the genus Nemadactylus 

Within the cirrhitoid fishes, five morphologically distinct 
types of urohyal can be recognised (Figs 1 & 2). Since each 



REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA 




Fig. 1 The urohyal of: A. Paracirrhites forsteri; Cirrhitidae; left lateral view (BMNH 1852.9.13: 119). B. Chironemus marmoratus; 

Chironemidae; left lateral and ventral views. (BMNH 1871.3.29:28). C. Aplodactylus punctatus; Aplodactylidae; left lateral and ventral 
views. (BMNH 1873.4.3: 157). D. Dactylophora nigricans; Cheilodactylidae; left lateral view. (BMNH 1869.2.24:8). Relative to other 
figures, this bone has been rotated through 90° to the left; arrow indicates dorsal prominence. Scale in millimetres. Drawn by Gordon 
Howes. 



type can be correlated with one of the five family groups 
recognised by Regan (1911), these will be referred to as the 
cirrhitid, latrid, chironemid, aplodactylid and cheilodactylid 
types respectively. 

The cirrhitid type (Fig. 1A) appears to be a plesiomorphic 
form, one fundamentally similar to that found in several basal 
percoids (see Kusaka, 1974; also personal observations). 

The latrid urohyal (Fig. 2) differs markedly from the 
cirrhitid type, and also shows slightly more intrafamilial 
variation, particularly with regard to its posterior margin's 
degree of indentation, the extent to which the ventral margin 
is produced bilaterally into a narrow or broader shelf, the 
extent to which the bone is produced ventrally, and whether 



the bone's upper margin is sharp or somewhat flattened. Like 
the cirrhitid type, the latrid urohyal is also of a pleisomorphic 
form, one occurring in such basal percoids as the Serranidae 
and Centropomidae (Kusaka, 1974; Greenwood, 1976: 39, 
fig. 21, and other personal observations). 

Departure from the basal percoid form of urohyal is most 
pronounced in the chironemid, aplodactylid and cheilodac- 
tylid types of bone. In chironemids (Fig. IB) the bone is 
shallow, the ventral margin greatly flattened and expanded 
bilaterally to form a broad shelf, while the dorsal margin is 
also noticeably flattened and bilaterally produced into a shelf, 
albeit one relatively narrower than that on the ventral aspect 
of the bone; when compared with the urohyal in cirrhitids, 



PH. GREENWOOD 







Fig. 2 The urohyal of four latrid species. A. Acantholatris monodactylus (BMNH unregistered; ex Gough Island); left lateral and ventral 
views. B. Latris lineata (BMNH 1855.9.19:194); left lateral view. C. Mendosoma lineatum (BMNH 1960.1.8:14-21); left lateral and ventral 
views. D. Latridopsis ciliaris (BMNH 1872.7.1:31); left lateral and ventral views. Scale in millimetres. Drawn by Gordon Howes. 



the chironemid type is relatively foreshortened (cf Figs 1A & 
IB). 

A pronounced ventral shelf and overall foreshortening of 
the bone is also characteristic of the aplodactylid urohyal 
(Fig. 1C), but in this type the bone is relatively deeper than is 
the chironemid urohyal, and the dorsal surface is produced 
into only a narrow shelf. 

When compared with all other types, the cheilodactylid 
urohyal (Fig. ID) is very distinctive. In lateral view it has 
virtually the shape of an arrow-head with its tip directed 
anteriorly, and with the two arms meeting at the somewhat 
thickened apex from which a dorsally directed process arises. 
The anterior edges of both arms are slightly broadened to 
form a very narrow bilateral shelf that does not quite extend 
to the posterior tip of either arm. Although, morphogeneti- 
cally, the cheilodactylid type of urohyal could be derived 



from a latrid type by a marked anterior extension and 
deepening of the latter's posterior indentation, coupled with 
an increase in the angle subtended by the two arms so 
formed, the two morphotypes are readily distinguishable. 
Interestingly, the urohyal in the so-called 'paperfish' juvenile 
stage (see p. 7) of a 44 mm standard length Cheilodactylus 
pixi Smith, 1980, resembles that of the latrid type more 
closely than does this bone in larger specimens; nevertheless, 
the upper and lower arms of the urohyal in the 'paperfish' 
stage are more widely separated, the division between them 
extends further anteriorly, and the anterior body of the bone 
is less compressed and more barrel-like than that in any of the 
adult latrid urohyals I have examined. 

In his monograph on urohyal bones Kusaka (1974) 
described and illustrates this bone in Goniistius zonatus 
(Cuv., 1839), a taxon now, and previously (Gill, 1862), 



REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA 



referred to the family Cheilodactylidae (see Allen & Heem- 
stra, 1976, for comments on the status of this genus; also p. 6 
below). Kusaka, however, lists the species under the heading 
Aplodactylidae. The bone depicted is certainly of the cheilo- 
dactylid type and not of the aplodactylid type, and I presume 
Kusaka's placing the species in the Aplodactylidae is a lapsus. 
This author (op. cit: ) also figured and described the urohyal 
from a specimen supposedly of Cirrhitichthys aureus Temm. 
& Schl., 1843 (Cirrhitidae). Unfortunately I have not been 
able to examine a specimen of this species, but the bone 
illustrated (and described as 'shaped like a standing rat') is 
unlike that in any cirrhitoid taxon I have examined, particu- 
larly amongst members of the Cirrhitidae and even in a taxon 
such as Oxychirrhites typus Bleeker, 1857, whose elongate 
and tubular snout is an unusual morphotype within both the 
Cirrhitidae and the cirrhitoids as a whole. If Kusaka's figure 
and description are accurate and the specimen was correctly 
identified, then a sixth and highly distinctive form of urohyal, 
one far removed from that of other cirrhitids must be 
recognised, and the higher taxonomic position of its possessor 
or posessord be reconsidered (assuming, that is, the bone 
Kusaka examined was not teratological or damaged during 
preparation). 

A typical cheilodactylid urohyal (Fig. ID) occurs in all 
members of the family (sensu Regan [1911] and subsequent 
authors) I have examined apart from Nemadactylus and 
members of the genus Acantholatris , viz the type species A. 
monodactylus (Carmichael, 1818), and the species A. gayi 
(Kner, 1869) and A bergi (Norman, 1937). 

Parenthetically it should be noted that A. gayi and A. bergi 
were both placed in the genus Cheilodactylus, and the family 
Cheilodactylidae, by Norman (1937). The former species was 
later transferred by Fowler (1945) to the genus Acantholatris, 
with no explanation given for the change, but was retained in 
the family Cheilodactylidae. Neither author appears to have 
been aware, however, that Gill (1862) had included Acantho- 
latris in his subfamily Latridinae. Mann (1954: 266) followed 
Fowler's generic and familial placing of A. gayi, and listed the 
species bergi under Acantholatris in the index to that publica- 
tion. The reader is there referred to page 266 of the text. No 
mention is made of A. bergi on that page, but on page 85 (op. 
cit.) Acantholatris bergi Norman (the author's name not 
enclosed in brackets) is listed amongst the Tnvasores del 
Atlantico'. Mann (op cit.) is thus the first author to employ 
this particular combination of names for the species. As 
noted earlier (p. 1) Regan did not include Acantholatris in 
any of his cirrhitiform families. 



The familial classification of Acantholatris Gill, 
1982 and Nemadactylus 

The urohyal in all three Acantholatris species examined, and 
in Nemadactylus macropterus, is virtually identical and differs 
markedly from that in the cheilodactylids, cirrhitids, aplodac- 
tylids and chironemids (see pp. 2-5 and cf Fig. 1 with Fig. 
2A). Instead, it resembles the latrid type, both in detail and 
in its gross morphology (c/Figs. 2A, B and C), especially in 
its fan-like outline. This marked difference would suggest 
1 that the latrid genera (as listed in Regan, 1911), together with 
1 Acantholatris and Nemadactylus shared a recent common 
ancestry distinct from that of the cheilodactylids. It also 
suggests that the phyletic relationships of the two groups are 
obscured by uniting the cheilodactylids with the latrids in a 



single subfamily, as did Gill (1862). 

Thus, in my view, based essentially on their urohyal 
morphology and not negated by other characters (see, how- 
ever, the pectoral fin character discussed below), Acanthola- 
tris and Nemadactylus should be included in the family 
Latridae, currently comprising species of the genera Latris, 
Latridopsis and Mendosoma, the latter recently shown to be 
monotypic by Gon & Heemstra (1987). In addition to the 
urohyal characters, the genera listed above lack a suborbital 
shelf, which in cheilodactylids is a prominent feature formed 
from the posterior upper margin of the lachrymal bone and 
the entire upper margins of the second and third suborbitals. 
Also, unlike cheilodactylids, these genera have the basal 
scaly sheath to the soft dorsal fin somewhat higher and thus 
more prominent than that at the base of the spinous part of 
the fin. 

As in cheilodactylids, the latrids (here taken to include 
Acantholatris and Nemadactylus) have 35 vertebrae (14 
abdominal + 21 caudal elements including the urostylar 
element; data from radiographs and dry skeletons listed on 
p. 2). To judge from the dry skeletal and dissected material 
available to me, parapophyses are present on all precaudal 
centra in both families, and no ribs are sessile. 

Possible lineages within the Latridae as now 
expanded to include the genera Acantholatris and 
Nemadactylus 

Acantholatris and Nemadactylus differ noticeably from Latris, 
Latridopsis and Mendosoma in having one of the lower, 
unbranched pectoral rays (i.e. the fifth, sixth or seventh ray 
from the bottom of the series) greatly elongated, its tip, 
which extends beyond the fin's margin, reaching to at least 
the level of the anus and sometimes as far as the midpoint of 
the anal fin. 
There are also differences in the following features: 

(i) In scale size, as shown by lateral-line scale counts. In 
Latris, Latridopsis and Mendosoma these range from 112 to 
120 in the two former taxa, and from 68-78 in Mendosoma 
(data from Last et. al, 1983; Gon & Heemstra, 1987; 
pers.obs.). In Nemadactylus macropterus the count is 59 or 
60, and in other species 47-68 (pers obs.; Last et. al., 1983) 
and in Acantholatris monodactylus, A. bergi and A. gayi the 
range is from 50-60 (Norman, 1937; pers. obs.). 
(ii) Anal fin length. In Latris, Latridopsis and Mendosoma, 
the number of branched anal rays ranges from 17-35 (the 
lowest counts occurring in Mendosoma, viz. 17-21, whereas 
in Acantholatris species and Nemadactylus macropterus the 
range is from 12-15, and other species of the genus, 16-19 
(sources as above). 

Pending a detailed generic revision of the various taxa 
involved, especially the several Australian and New Zealand 
species currently referred to the genus Nemadactylus it would 
be premature to formally recognise the two groups as, for 
instance, tribes or subfamilies of the Latridae, although 
phylogenetically some split seems to have occurred within the 
lineage. 

The condition of the pectoral fin in the Latris- Latridopsis- 
Mendosoma group of latrids provides something of a puzzle 
since these taxa are the only cirrhitiforms not showing any 
marked elongation of the uppermost unbranched ray in the 
lower section of the pectoral fin, nor, as in most other 



PH. GREENWOOD 



cirrhitoids, do any of these rays clearly extend beyond the fin 
membrane, and none is markedly thickened. In having the 
lowermost 5-9 rays unbranched, these fishes are, however, 
typically cirrhitoid. This latter condition can be considered 
one of the synapomorphies uniting cirrhitoid fishes. 

A typically derived pectoral fin configuration occurs in 
the Cirrhitidae, yet the family would appear to be the least 
derived of all cirrhitoid taxa (see p. 8). In contrast, except 
for the condition of the pectoral fin, members of the 
Latris-Latridopsis-Mendosoma assemblage within the 
Latridae share with Acantholatris and Nemadactylus, and 
with the cheilodactylids, aplodactylids and chironemids, 
the derived condition for all the osteological and myologi- 
cal features discussed on page 5. That being so, it is 
unlikely that the pectoral fin form in Latris, Latridopsis 
and Mendosoma can be interpreted as a true retention of 
the plesiomorph condition. If that was the case, then the 
derived condition must have evolved more than once 
within the cirrhitoids. A more parsimonious solution to the 
problem therefore, would, be to interpret the pectoral fin 
form in Latris, Latridopsis and Mendosoma as a secondary 
reversal to a seemingly more plesiomorphic condition than 
is found in any other cirrhitiforms, including the family 
with the greatest number of plesiomorphic features, the 
Cirrhitidae (see p. 8). 

The geographical distribution of the two groups within 
the Latridae has an interesting pattern. Of the taxa in the 
long-finned assemblage, Nemadactylus (see p. 5) occurs 
only in Australia, Tasmania and New Zealand, thus over- 
lapping the entire range of Latridopsis a member of the 
short-finned group and one restricted to that region; it 
overlaps in part (New Zealand and Tasmania) that of the 
widely distributed Mendosoma lineatum, also a member of 
the short-finned group, and in part, that of Latris, another 
member of the short-finned group (Australia; New 
Zealand; Gough and Tristan da Cunha islands; Vema 
Seamount; St Paul and Amsterdam islands). The other 
long-finned taxon, Acantholatris , does not occur in Aus- 
tralasia, but has a wide western distribution, including St 
Paul, Amsterdam, and Gough Islands, Tristan da Cunha, 
Vema Seamount Chile, Juan Fernandez and the western 
coast of South America from Rio de Janeiro southwards. 
This distribution thus widely overlaps that of the short- 
finned, monotypic genus Mendosoma lineatum, viz St Paul, 
Amsterdam and Gough islands, the coast of Chile and, as 
noted above, New Zealand and Tasmania (the latter being 
areas where Acantholatris does not occur); data from 
Norman, 1937; Fowler, 1945; Mann, 1954; Smith 1984; 
Last et. al., 1983; Gon & Heemstra, 1987; Paulin et. al. 
1989; Andrew & Hecht, 1992; Andrew, pers.comm., 1993). 



TAXONOMIC AND PHYLOGENETIC 
CONCLUSIONS 



Taxonomy 

The material studied indicates, on osteological and myologi- 
cal grounds (p. 5), that the species currently named Nema- 
dactylus macropterus (the type species of Gill's (1862) genus 
Dactylopagrus; see Wheeler, 1986) should be classified in the 
Latridae and not the Cheilodactylidae as it is at present. 



The genus Acantholatris Gill (1862, type species Chaetodon 
monodactylus Carmichael, 1818), was overlooked by Regan 
(1911) in his synoptic review of cirrhitoid families, but is 
currently placed in the family Cheilodactylidae (see p. 5). 
However, on the basis of its urohyal morphology, and its 
lacking a suborbital shelf (see p. 5) the genus should be 
classified in the Latridae. Regan (1911) differentiated the 
Latridae from the Cheilodactylidae on the basis of the latrids 
having feeble, unbranched pectoral rays that are not pro- 
duced beyond the fin's margin, and by their lacking a 
suborbital shelf; in other feaures he noted that the two 
families are similar. With the inclusion of Acantholatris and 
Nemadactylus in the Latridae the nature of the pectoral fin no 
longer serves as a differentiating feature (see p. 5), the 
principal diagnostic characters for the family now lying in the 
form of the urohyal bone, the absence of a suborbital shelf, 
and in the more prominent arrangement of the basal sheath- 
ing scales of the soft dorsal fin (see p. 5). 

Gill's (1862) suprageneric classification included Nemadac- 
tylus as a division - Nematodactyli - of his subfamily Latridi- 
nae, in which subfamily but as another division to which he 
gave the name Latrides he also included Latris, Latridopsis, 
Mendosoma, Acantholatris, Chirodactylus, Cheilodactylus 
and Goniistius. Regan (1911) on the other hand, but without 
reference to Gill's paper, treated the latter author's four 
subfamilies as families, and recognised a fifth, the Cheilodac- 
tylidae, for two genera, viz Cheilodactylus and Nemadactylus; 
no mention is made in Regan's paper of the other taxa in 
Gill's Latridinae except for Latris and Mendosoma, which 
Regan retained in his family Latridae. 

The evidence presented here (pp. 2-5), especially that 
based on urohyal morphology, would support Regan's (1911) 
classification with regard to the separation of Cheilodactylus 
(and, although not mentioned by Regan, Chirodactylus and 
Goniistius) from the other taxa included in Gill's Latridinae, 
and would support the inclusion of all three taxa in one 
family, the Cheilodactylidae. The same evidence would also 
support Gill's inclusion of Latris, Latridopsis, Acantholatris, 
Mendosoma and Nemadactylus in a single suprageneric 
taxon. Since Regan's (1911) familial ranking has been 
accepted and used since that time, and until contraindicative 
evidence is available to suggest otherwise, that ranking (i.e. 
Latridae) is retained. 

The anatomical and other features used in this paper 
(pp. 2-5) would support the recognition of Gill's (1862) and 
Regan's (1911) other suprageneric lineages, again, for the 
reasons given above, as families and not subfamilies, viz. the 
Cirrhitidae, Aplodactylidae (Gill's Haplodactylinae) and Chi- 
ronemidae. 

At an intrafamilial taxonomic level, Allen & Heemstra 
(1976) note that 'The currently accepted classification of the 
Cheilodactylidae ... is most unsatisfactory' a sentiment I 
would not only endorse, but would extend to other cirrhiti- 
form families as well. In part this situation has resulted from 
the use of mainly superficial characters, with little or no 
attention paid to anatomical features, especially myological 
and osteological ones. Thus on those grounds I cannot agree 
with Allen & Heemstra's (op.cit.) treating Acantholatris as a 
subjective synonym of Cheilodactylus and its consequent 
placement in the Cheilodactylidae (see above, p. 5). How- 
ever, at least on the characters and specimens I have exam- 
ined, I would endorse their synonymy of Whitley's (1957) 
genus Morwong (type species Cheilodactylus fuscus Castel- 
nau, 1879) with Cheilodactylus. 






REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA 



The cirrhitoids as a monophyletic lineage 

On the basis of several apparently synapomorphic character- 
istics (see below) the cirrhitoids would seem to be a mono- 
phyletic lineage, a conclusion implied by both Gill (1862) and 
Regan (1911) who described the group as a 'natural' one but 
gave no reasons for that conclusion. The derived characters 
on which I would base an hypothesised monophyly of the 
cirrhitoids are, taken in conjunction, a reduced number (15) 
of principal caudal fin rays, the unbranched lowermost five to 
nine rays in the pectoral fin (usually with their tips produced 
beyond the fin membrane), the lower part of each cleithrum 
greatly expanded anteroposteriorly and meeting its antimere 
in a deep, carinate symphysis, an increased number of 
vertebrae relative to other percoids (26-35, comprising 10-16 
abdominal and 15-21 caudal elements), and the presence, 
ventrally, in subadults of a peculiar, lipoid-filled sac (Fig. 3), 
free from the overlying hypaxial muscles, and extending from 
the urohyal, to which it is attached, to the anus, with the 
lipoidal material apparently contained in hexagonal compart- 
ments. 

To the best of my knowledge, this lipoid sac has not previ- 
ously been noted as a feature of subadult cirrhitoid fishes, nor 
indeed of any other perciforms except the stichaeid Lumpenus 
maculatus (see Falk-Petersen et al., 1984). I first observed it in 
small specimens (the so-called 'paperfish' stage) of Cheilodacty- 
lus pixi ca 43 to 44 mm standard length (Fig. 3), where its 
presence results in the 'pouter-pigeon'-like ventral profile of the 
paperfish stage in this and other cirrhitoid species (see photo- 
graphs in Whitley, 1957; Allen & Heemstra, 1976, and Nielsen, 
1963). Subsequent dissections revealed a lipoid sac in members 



of all but two of the cirrhitoid families I have dissected (see 
p. 2). The exceptions are a chironemid, Chironemus marmora- 
tus Giinther, 1860 (160 mm standard length) and an aplodac- 
tylid, Aplodactylus lophodon Giinther, 1859 (180 mm S.L.). 
Since, however, the sac is a juvenile (i.e. sub-adult) feature in 
the other taxa, and the exceptional specimens were, to judge 
from their gonadial development, young adults, I suspect that it 
would also be present in smaller specimens of these species. In 
Cheilodactylus pixi, for example, the sac is well-developed in a 
specimen of 44 mm standard length, but has disappeared in one 
of 46 mm. Likewise, in Chirodactylus brachydactylus (Cuv., 
1830), it is present in a fish of 38 mm standard length, but absent 
in one of 42 mm. The presence of a lipoid sac in specimens from 
128 to 243 mm standard length of other species (referred in the 
current literature to the Latridae and Cheilodactylidae) whose 
maximum adult lengths are from 50 cm to one metre, suggests 
that the size at which the lipoid sac disappears is positively 
correlated with that at which members of a species become 
adult. This supposition is borne out by the presence of the sac in 
a juvenile Chirodactylus grandis (Giinther, 1860) of 57 mm 
standard length, a species whose adults reach a length of one 
metre, whereas it has disappeared, at a length of 42 mm, in 
young Chirodactylus brachydactylus, whose adults reach a 
length of 40 cm. Again, it is present in a specimen of Acanthola- 
tris monodactylus 243 mm S.L.; adults of this species attain a 
standard length of at least 65 cm. Thus, the sac's apparent 
absence in chironemids and aplodactylids could be artef actual, 
and related to the size-range of the specimens I was able to 
examine. 

It is hoped to carry out a more detailed examination of the 
lipoid sac when specimens suitably fixed for detailed histo- 




Fig. 3 Chirodactylus pixi, 49 mm standard length (RUSI 19842) in right lateral view; partially dissected, and with the greater part of the 
pectoral and the entire pelvic fin removed. The large anterior portion of the lipoid sac (LS) is clearly visible; part of its posterior portion is 
also visible (x). Throughout its length, the wall of the sac, unlike the muscles above it, is heavily peppered with melanophores. 



P.H. GREENWOOD 



logical and histochemical study are available. 

Intragroup relationships within the cirrhitoids, 
and the ranking of the group 

Within the cirrhitoids, the Cirrhitidae should be ranked as the 
most plesiomorphic taxon, a view seemingly implicit in 
Regan's (1911) diagram of relationships. My reasons for 
giving the family this ranking are based on urohyal form, the 
low vertebral count (26-28) relative to that in other families, 
the absence of parapophyses on the first three abdominal 
vertebrae, sessile ribs associated with these vertebrae, the 
presence of 3 predorsal bones (2 in the other cirrhitoids 
radiographed or dissected) and the presence of a suborbital 
shelf (which, however, is also developed in the Cheilodactyl- 
idae [but see below]). Furthermore, the Cirrhitidae are the 
only cirrhitoids with a basal percoid type of myotome 
arrangement in the sternohyoideus muscle, a feature not 
previously noted. That is, one in which the three pairs of 
hypaxial myomeres forming the sternohyoideus muscle are all 
arranged in a vertical series, with the first block covering the 
anterior part of the urohyal (Fig. 4A). Members of all other 
cirrhitoid families, in contrast, have the first (i.e. anterior) 
hypaxial myotome of each side displaced ventrally so that it 
now lies medially and horizontally (not, as in cirrhitids, 
laterally and vertically) to form, with its antimere, a ventral 
muscle, paired in most species but in some with the left and 
right parts fused over most of their lengths to form a single 
median muscle (Fig. 4B). Single or paired, this ventro-medial 
component of the sternohyoid runs from the urohyal tip to 
the prominent ventral projection at the symphysis of the left 



and right cleithra, its origin thus being immediately before 
that of the anterior infracarinalis muscle insertion. 

In both the Cirrhitidae and in the other families, the 
sternohyoideus myotomes, except the horizontal first myo- 
tome in the latter group, are chevron-shaped with the apex 
directed anteriorly. However, in the latrids, cheilodactylids, 
chironemids and aplodactylids, the angle between the upper 
and lower arms of the chevron is more acute, and the lower 
arm is relatively longer than in cirrhitids. 

Judging from the rather scant literature on the sternohyoid 
muscle in teleosts (see Winterbottom, 1974), and from a 
personal knowledge of the situation in percoids, the condition 
of the muscle in the Cirrhitidae should be ranked as plesio- 
morphic, that in the other cirrhitoid families as derived and 
possibly a unifying synapomorphy for the Aplodactylidae, 
Chironemidae, Latridae and Cheilodactylidae within the lin- 
eage. 

In Regan's (1911) figure of cirrhitoid intrarelationships 
referred to above, the Cirrhitidae occupy a basal (i.e. stem 
position) and are linked, on the one hand to the Chironemi- 
dae and Aplodactylidae, and on the other to the Cheilodac- 
tylidae and Latridae (the generic composition of the families 
being those given by Regan). No reasons were provided by 
Regan for these supposed relationships, which presumably 
were based mainly on superficial characters as well as a few 
anatomical ones. With the anatomical information now avail- 
able a different scheme of intragroup relationships at the 
family level can be proposed (see Fig. 5, and Table 1). 

In this scheme, apomorphic features (see Table 1) are 
taken to be: (i) The derived form of urohyal, of which there 
are three distinct types (see p. 3). (ii) The presence of a 




ce 



Fig. 4 A. Cirrhitid type organization of sternohyoid 
myotomes. Drawn from Paracirrhites forsteri; 
semi-schematic. In this arrangement, the 
sternohyoid muscles completely envelop the urohyal 
bone. B. Basic organization of the sternohyoid 
myotomes in all other families. Drawn from 
Nemadactylus monopterus; semi-schematic. In taxa 
of these families, varying an terior extents of the 
urohyal are not covered by the sternohyoid muscle. 
1-4: 1st to fourth myotomes of the sternohyoid 
muscle; c: cleithrum; ce: cut edges of the sterno- 
hyoid myotomes; uh: urohyal. Drawn by Anthea 
Ribbink 



B 




ce 



REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA 



sJt? 



.v6' 



• 



x6 fl 



>* 



** 



4 ,15 | 



,15*1 



A? 



3*. 15*| 



O* 



7* 1 1*. 1 3* 



1 or 2,6,8,10,12,14 



Fig. 5 Tentative scheme of phyletic relationships within the Cirrhitoidei. Asterisks indicate apomorphic characters (see also Table 1). Since 
both the cirrhilid (1) and latrid (2) condition of the urohyal are rated as pleisomorphic, that bone in the common ancestor of all lineages is 
taken to be 1 or 2. 



derived myotomal arrangement of the sternohyoideus 
muscles (p. 8). (iii) More than 28 vertebrae, (iv) Parapophy- 
ses developed on the first three abdominal vertebrae, with 
the first pleural rib associated with the second or third 
vertebrae, (v) Predorsal bones reduced to 2. The three 
different types of derived urohyal morphology (pp. 2-5) (ie in 
chironemids, aplodactylids and cheilodactylids) are each 
taken to be independently evolved apomorphies. Relation- 
ships (Fig. ) suggested by these data are: (i) That the 
cirrhitids are the plesiomorph sister group to the other four 
families combined, (ii) The chironemids are the sister taxon 
of the aplodactylids, latrids and cheilodactylids combined, 
and that for the moment this assemblage should be treated as 
an unresolved trichotomy since no two lineages uniquely 
share a recognisable synapomorphic feature. For example, 
the urohyal in the latrids is of a basal percoid type, and 
although that bone in the cheilodactylids and aplodactylids is 
highly derived, each is unique to the families respectively. 
The cheilodactylids it will be noted, retain the plesiomorphic 
suborbital shelf, whereas it is lost in the latrids and aplodac- 
tylids (and in the chironemid lineage as well). The value of 
this feature as an indicator of relationship, however, is 
problematical because it involves a loss (and not an acquisi- 
tion) in the lineages concerned. Clearly, a greater number 
and variety of characters must be sampled and their polarity 
determined before this hypothesis of cirrhitoid intrarelation- 
ships can be improved and the trichotomy resolved. 

The same reservation would apply before any sister-group 
hypothesis can be erected regarding the relationships of the 
cirrhitoids within the Percomorpha. However, based on the 



synapomorphic features discussed (above pp. 6-7) it seems 
reasonable to hypothesize that the five families comprising 
the lineage, given informal ranking as the 'cirrhitiform per- 
coids' by Regan (1911), and suprafamilial status by recent 
authors (Nelson, 1994), should be elevated to subordinal 
status (Cirrhitoidei) within the Perciformes. 



Acknowledgements. I am particularly indebted to Dr Colin Buxton 
of Rhodes University's Department of Ichthyology and Fisheries 
Science who first aroused my interest in the anatomy of cirrhitoid 
fishes, and who provided many specimens for dissection. Professor 
Tom Hecht of that department is to be thanked for personally 
obtaining a specimen of Cheilodactylus fuscus from Salamander Bay, 
New South Wales, in which operation he was aided by Bill Talbot of 
the Brackish Water Fish Culture Research Station there. 

To Dr Phil Heemstra of the J.L.B. Smith Institute goes my 
gratitude for the many discussions we have had about cirrhitoids, and 
for his advice on the relevant literature, and to Tony Booth of DIFS 
my appreciation for his painstaking preparation of several skeletons. 
Once again it is a great pleasure to thank my old colleague Gordon 
Howes for his elegant and accurate draftmanship, and also to thank 
another former colleague, Oliver Crimmen of the Fish Section, The 
Natural History Museum, London for his untiring help with matters 
radiographic and bibliographical. Yet again, my special thanks go to 
Huibre Tomlinson, for her patience and skills in producing the 
typescripts, and to Robin Stobbs for producing certain of the 
radiographs, and the photograph, used in this paper. 



10 



PH. GREENWOOD 



Table 1 Data matrix and characters. 





1 


2 


3 


4 


5 


6 


7 


8 


9 


10 


11 


12 


13 


14 


15 


Cirrhtidae 
































Amblycirrhitus pinos 


+ 














+ 





+ 





+ 





+ 





+ 





Cirrhitus maculatus 


+ 














+ 





+ 





+ 





+ 





+ 





Cirrhitichthys oxycephalic 


+ 














+ 





+ 





+ 





+ 





+ 





Cyprinocirrhites polyactus 


+ 














+ 





+ 





+ 





+ 





+ 





Gymnocirrhites arcatus 


+ 














+ 





+ 





+ 





+ 





+ 





Oxycirrhites typus 


+ 














+ 





+ 





+ 





+ 





+ 





Paracirrhites forsteri 


+ 














+ 





+ 





+ 





+ 





+ 






Chironemidae 

Chironemus marmoratus 

Latridae 

Acantholatris bergi 

A. gayi 

A. monodactylus 

Latridopsis ciliaris 

Latris lineata 

Mendosoma lineatum 

Nemadactylus macropterus 

Aplodactylidae 

Aplodactylus punctatus 
A. lophodon 

Cheilodactylidae 

Cheilodactylus fasciatus 

C. fuscus 

C. pixi 

C. zonatus 

Chirodactylus brachydactylus 

C. grandis 

Dactylophora nigricans 






+ 














+ 





+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





e- 




+ 








+ 











+ 





+ 





+ 





+ 





+ 








+ 











+ 





+ 





+ 





+ 





+ 














+ 





+ 





+ 





+ 





+ 


+ 

















+ 





+ 





+ 





+ 





+ 


+ 

















+ 





+ 





+ 





+ 





+ 


+ 

















+ 





+ 





+ 





+ 





+ 


+ 

















+ 





+ 





+ 





+ 





+ 


+ 

















+ 





+ 





+ 





+ 





+ 


+ 

















+ 





+ 





+ 





+ 





+ 


+ 






Characters: 1. Cirrhitid-type urohyal (i.e. of a basal percoid type, but one differing from the latrid condition); 2. Latrid-type urohyal (i.e. of 
basal percoid type; see 1); *3. Aplodactylid-type urohyal; *4. Chironemid-type urohyal; *5. Cheilodactylid-type urohyal; 6. Less than 28 
vertebrae; *7. More than 28 vertebrae; 8. Parapophyses not developed on the first three (sometimes 4) abdominal vertebrae, but sessile 
pleural ribs on one or two of these centra; *9. Parapophyses developed on the first three abdominal vertebrae. No sessile pleural ribs; 1st 
pleural rib articulating with the parapophyses of the third abdominal vertebrae; 10. Three predorsal bones; *11. Two predorsal bones; 12. 
Basal percoid-type of sternohyoid muscle; *13. Derived condition of the sternohyoid muscle; 14. Suborbital shelf present; *15. Suborbital 
shelf absent. Asterisk indicates an apomorphic feature. 



REFERENCES 



Allen, G.R. & Heemstra, P.C. 1976. Cheilodactylus rubrolabiatus , a new 
species of Morwong (Pisces:Cheilodactylidae) from Western Australia, with 
a key to the Cheilodactylid fishes of Australia. Records of the Western 
Australian Museum, 4(4): 311-325. 

Andrew, T.G. & Hecht, T. 1992. Feeding biology of Acantholatris monodacty- 
lus (Pisces:Cheilodactylidae) at Tristan da Cunha and Gough Island, South 
Atlantic. South African Journal of Antarctic Research, 22: 41-49. 

Bloch, M.E. & Schneider, J.G. 1801. Systema ichthyologia. 584 p. Berolini. 

Falk-Falk-Petersen, S., Falk-Petersen, I-B, & Sargent, J.R. 1986. Structure and 
function of an unusual lipid storage organ in the arctic fish Lumpenus 
maculatus Fries. Sarsia, 71: 1-6. 

Fowler, H. W. 1945. Fishes of Chile. Systematic catalog. Apartado de la Revista 
de Historia Natural, Anos XLV-XLVII: 1-171. 

Gill, T.H. 1862. Synopsis of the family of cirrhitoids. Proceedings of the 
Academy of Natural Sciences of Philadelphia 14: 102-124. 

Gon, O. & Heemstra, P.C. 1987. Mendosoma lineatum Guichenot 1848, first 
record in the Atlantic Ocean, with a re-evaluation of the taxonomic status of 
other species of the genus Mendosoma (Pisces, Latridae). Cybium 11 (2): 
183-193. 

Greenwood, P.H. 1976. A review of the family Centropomidae (Pisces, 
Perciformes). Bulletin of the British Museum (Natural History) Zoology 29: 
1-81. 

Kusaka, T. 1974. The urohyal of fishes, xiv + 320 p. University of Tokyo Press, 
Tokyo. 

Last, P.R., Scott, E.O.G. & Talbot, F.H. 1983. Fishes of Tasmania, viii + 563 



p. Tasmanian Fisheries Development Authority, Hobart. 
Mann, G. 1954. Vida de los Peces en aguas Chilenas. 342 p. Ministero de 

Agricultura and Universidad de Chile, Santiago. 
Nelson, J.S. (1994). Fishes of the world; 3nd edition, xvii + 600 p. J. Wiley & 

Sons, New York. 
Nielsen, J.G. 1963. On the development of Cheilodactylus variegatus Valenci- 
ennes, 1833 (Cheilodactylidae) Copeia 1963(3): 528-533. 
Norman, J.R. 1937. Coast fishes, part II. The Patagonian Region. Discovery 

Reports. 16: 1-150. 
Paulin, C, Stewart, A., Roberts, C. & McMillan, P. 1989. New Zealand fish, a 

complete guide. National Museum of New Zealand, Miscellaneous Series., 

no. 19: xiv + 279. 
Regan, C.T. 1911. On the cirrhitiform percoids. Annals and Magazine of 

Natural History (8)7: 259-262. 
Smith, M.M. 1984. Cheilodactylidae. In: Fishcher, W. & Bianchi, G. (eds). 

FAO identification sheets for fishery purposes, western Indian Ocean. F.A.O. 

Rome. 
Wheeler, A.C. 1986. Catalogue of the natural history drawings commissioned 

by Joseph Banks on the Endeavour voyage 1768-1771, held in the British 

Museum (Natural History). Part 3: Zoology. Bulletin of the British Museum 

(Natural History) Historical Series 13: 1-172. 
Whitley, G.P. (1957). Ichthyological illustrations. Proceedings of the Royal 

Zoological Society of New South Wales, 1955-56: 56-71. 
Winterbottom, R. 1974. A descriptive synonymy of the striated muscles of the 

Teleostei. Proceedings of the Academy of Natural Sciences of Philadelphia 

125: 225-317. 






Bull. nat. Hist. Mus. Lond. (Zool.) 61(1): 11-90 Issued 29 June 1995 

Studies on the deep-sea Protobranchia 
(Bivalvia); the Subfamily Yoldiellinae 

J.A. ALLEN 

University Marine Biological Station, Millport, Scotland KA28 OEG 

H.L. SANDERS 

Woods Hole Oceanographic Institution, Woods Hole, Mass., 02543, U.S.A. 

F. HANNAH 

University Marine Biological Station, Millport, Scotland KA28 OEG 

CONTENTS 

Synopsis 12 

Introduction 12 

Subfamily Yoldiellinae Allen & Hannah, 1986 13 

Genus Yoldiella Verrill & Bush, 1897 13 

Yoldiella lucida (Loven, 1846) 13 

Yoldiella obesa obesa (Stimpson, 185 1 ) 15 

Yoldiella obesa incala ( new subspecies) 19 

Yoldiella similiris (new species) 20 

Yoldiella hanna (new species) 22 

Yoldiella capensis (new species) 23 

Yoldiella bilanta (new species) 24 

Yoldiella artipica (new species) 25 

Yoldiella similis (new species) 26 

Yoldiella sinuosa (new species) 27 

Yoldiella blanda (new species) 29 

Yoldiella biscayensis (new species) 30 

Yoldiella lata (Jeffreys, 1876) 32 

Yoldiella frigida (Torrell, 1859) 36 

Yoldiella robusta (new species) 39 

Yoldiella extensa (new species) 41 

Yoldiella inconspicua inconspicua Verrill & Bush, 1898 41 

Yoldiella inconspicua africana ( new subspecies) 44 

Yoldiella inconspicua profundorum (new subspecies) 45 

Yoldiella argentinensis (new species) 46 

Yoldiella curta Verrill & Bush, 1898 47 

Yoldiella perplexa (new species) 51 

Yoldiella americana (new species) 52 

Yoldiella subcircularis (Odhner, 1960) 54 

Yoldiella biguttata (new species) 57 

Yoldiella ovata (new species) 59 

Yoldiella insculpta (Jeffreys, 1879) 60 

Yoldiella Jeffrey si (Hidalgo, 1877) 63 

Yoldiella enata (new species) 68 

Yoldiella ella (new species) 70 

Yoldiella fabula (new species) 73 

Yoldiella veletta (new species) 76 

Genus Portlandia (Morch, 1857) 77 

Portlandia lenticula (Moller, 1842) 77 

Portlandia fora (new species) 78 

Portlandia minuta (new species) 80 

Portlandia abyssorum (Knudsen, 1970) 81 

Discussion 82 

References 90 



) The Natural History Museum, 1995 



12 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



Synopsis. Four species of the genus Portlandia and twenty-nine species and five subspecies of the genus Yoldiella 
from the deep Atlantic are described - many for the first time. The subfamily Yoldiellinae includes more species 
than any other higher taxon of deep-sea protobranchs. The differences in morphology are for the most part subtle 
and there are many closely related species. These close relationships have been analysed, the analysis taking into 
account shell shape, hinge morphology, musculature and the extent and course taken by the hindgut. Taken 
together with geographical and depth distribution a pattern of evolution is derived. This supports the view that the 
derivation of the deep-water species of Yoldiella in the Atlantic has been derived mainly via downslope migration 
and speciation rather than by deep water migration from the Southern Ocean. 



INTRODUCTION 



This is the eighth paper in a series on the biology and ecology 
of the deep-sea protobranch bivalves of the Atlantic (Allen & 
Sanders, 1973, 1982; Allen & Hannah (1989); Rhind & Allen 
(1992); Sanders & Allen 1975, 1977, 1985. Our interest is 
widespread and includes, ecology and adaptations to life at 
great depths, morphology, reproduction, distribution and 
evolution. Here we turn to the subfamily Yoldiellinae and 
what has become our major and most difficult task of all our 
protobranch studies to date. Nowhere have the problems of 
elucidating evolutionary trends and specific and subspecific 
divisions within the Protobranchia been so acute as in this 
large group. Of necessity descriptive and taxonomic studies 
have played a major role in all our studies. This is because so 
many species from the deep oceans are new. Now that we 
have studied more than three quarters of the protobranch 
material in our collections, it has become obvious that major 
questions on the evolution of the subclass - particularly those 
taxa in the deep ocean - remain to be answered. We have 
described (Sanders & Allen, 1985) intra- and inter- 
population variations in various species and the difficulties in 
separating even higher taxa with satisfactory, clear cut, 
definitions (Allen & Hannah, 1986). These difficulties can be 
no better illustrated than in our studies on the Yoldiellinae. A 
considerable effort has been put into the analysis of the most 
subtle differences in shape and form of the many species of 
the subfamily. As a consequence we have decided to record 
our observations in two parts. In the first, here, we describe 
36 species in a way that has become standard for this series of 
papers, describing those population variations that are perti- 
nent to description and taxonomy. In the second, we will 
report in detail on diversity and the quantitative aspects of 
the ecology of sibling species which are distributed widely in 
many Basins of the Atlantic. 

Species of the subfamily Yoldiellinae, are among the most 
common protobranchs of the deep sea and many are recorded 
in the literature. The difficulties we have experienced in 
accurately distinguishing the species is not new and confusion 
is apparent in both past and recent literature and in museum 
identifications of this group. 

Descriptions of genera and higher taxa are based on the 
recent studies of Shileiko (1985) and Allen & Hannah (1986), 
but complemented from the results of this study. Holotypes 
have been lodged in either the Natural History Museum, 
London, or the Museum National d'histoire Naturelle, Paris. 
The paratypes, together with the remainder of the specimens 
collected, for the time being are in the care of JAA, but at the 
conclusion of the studies will be lodged in appropriate 
Museums. 

Measurements of height, length, width and postumbonal 



length have been taken and in the case of larger samples 
ratios have been plotted. For species of which we have few 
specimens the measurements have been tabulated. While 
these record the variation in the major axes, they do not 
measure subtle variation in shell outline and curvature. Much 
time has been spent on computerized analysis of shell shape 
and on this work we hope to report later but, to date, this has 
not improved on visual recognition from comparative accu- 
rate drawings. We prefer drawings to photographs for their 
clarity. 

In recognizing subspecies we comply with the ICZN. 
Subspecies occur at different depth ranges and/or different 
basins. In a few cases we recognize 'forms', infrasubspecific 
units which, in compliance with ICZN, cannot clearly be 
distinguished in their distribution patterns but which may 
indicate a species in the process of subspeciation. 



ABBREVIATIONS TO TEXT FIGURES 


AA anterior adductor muscle 


ME mantle edge 


AN anus 


MT major typhlosole 


AS anterior sense organ 


NV nerve 


BG 'byssal' gland 


OE oesophagus 


CG cerebral ganglion 


PA posterior adductor muscle 


CS combined siphon 


PG pedal ganglion 


DD digestive duct 


PL palp 


EG digestive diverticula 


PM pallial muscles 


DH dorsal hood 


PP palp proboscis 


ES exhalent siphon 


PR pedal retractor muscle 


FA feeding aperture 


PSA posterior sorting area 


FM pedal muscles 


RM longitudinal muscle 


FT foot 


SC statocyst 


GC gland cells 


SE siphonal embayment 


GD duct of gland 


SF sole of foot 


GI gill 


SS style sac 


GS gastric shield 


ST stomach 


HG hind gut 


SY fold of sensory organ 


HT heart 


TE tentacle 


IF inner muscular fold 


TM transverse muscle 


IS inhalent siphon 


TS tooth of gastric shield 


LI ligament 


VG visceral ganglion 



Family Nuculanidae Adams & Adams 1858 

Shell elongate, usually moderately compressed, may be ros- 
trate, shell gape if present, restricted to short posterior 
margin where siphons protrude, concentric sculpture usually 
present which may be strongly incised, middle and inner shell 
layers non-nacrous; teeth chevron-shaped; ligament internal 
or external with resilium; combined siphons present, usually 
a simple siphonal tentacle attached to the left or right side of 
the siphonal embayment. 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



13 




Fig. 1 Yoldiella lucida. Lateral views of 
shells of different size seen from the 
right side to show variation in shell 
outline. Collected by R.V. Dana 1922; a 
& b, 50°20'N 9°00'E, 350 m; c & d, 
58°13'N, 9°34'E, 650 m. (Scale = 1.0 
mm). 



Subfamily Yoldiellinae Allen & Hannah 1986 

Shell small, usually compressed, ovate or elongate subovate, 
occasionally with ill-defined rostrum, not gaping, smooth, or 
very fine concentric sculpture; ligament amphidetic, largely 
internal; combined siphons with various degrees of tissue 
fusion, siphonal embayment small; hind gut with various 
configurations. 



Genus Yoldiella Verrill & Bush 1897 

Type species. By original designation, Yoldia lucida Loven, 
1846. 

Shell small, fragile, usually slender, subovate, usually 
glossy, no escutcheon or lunule, no carina, not gaping, 
occasionally fine concentric sculpture, postero-ventral margin 
may be slightly sinuate, postero-dorsal margin usually slightly 
convex, maybe posteriorly angulate; umbo usually anterior 
occasionally posterior or central; chevron-shaped hinge teeth 
may or may not extend beyond the inner limit of adductor 
muscles; no chondrophore; except for very small external 
componant, ligament internal and amphidetic, but may 
extend anteriorly and/or posteriorly to a small degree, hind- 
gut with various configurations, mostly deep-water species 
beyond shelf-slope break. 

Note. A detailed account of an internal morphology is given under 
Y. lata (p. 34). 



Yoldiella lucida (Loven 1846) 

Type locality. Hammerfest, northern Norway (desig. A. 
Waren, 1989). 

Type specimen. Lectotype (desig. A. Waren, 1989), Swed- 
ish Museum of Natural History, No. 1533. 

Yoldia lucida Loven 1846, p. 34. 



Leda lucida Jeffreys 1869, p. 173. pi. 100, Fig. 1; Jeffreys 

1879, p. 578;Locard 1898, p. 351, 362. 
Portlandia lucida Sars G.O. 1878, p.37. pi. 4, Figs. 8a, 8b; 

Norman 1893, p. 364; Posselt 1898, p. 36; Ockelmann 

1958, 122, p. 29. 
Yoldiella iris Verrill & Bush 1898, 20, p. 863-864, pi. 80. Fig. 

1,2, pi. 82, Fig. 11; Type specimen U.S., Natl. Mus. 

159722. 
Yoldiella lucida Tebble 1966, p. 29, Fig. 156. 

Material. 



Cruise Sta Depth No 


Lat 


Long 


Geai 


• Date 


(m) 










NORWEGIAN BASIN 










Thor 273 610 










350 50 


58°20'0N 


09°00'0E 






Dana 2896 60 


58°13'0N 


09°34'0E 






NORTH AMERICAN BASIN 










Chain 58 105 530 124 


39°56'6N 


71°03'6W 


ET 


5.5.66 


Chain 88 207 805- 264 


39°51'3W 


70°54'3W 


ES 


21.2.69 


811 


39°51'0W 


70°56'4W 






WEST EUROPEAN BASIN 










Incal DS03 609 2 


57°57'0N 


10°43'0W 


CP 


16.7.76 


DS04 619 1 


57°58'0N 


10°43'0W 


CP 


16.7.76 



Museum material examined is listed in the text. 

Specimens of Yoldiella lucida have most subtle differences 
in shape that taxed the descriptive powers of our predecessors 
and as they do ours. Jeffreys (1879) recognized three varieties 
{lucida, declivis and truncatd) while Locard (1898), accepting 
the form figured by Sars (1878) as the type, recognized five 
varieties (truncata - the form figured by Jeffreys, intermedia, 
minor, depressa, and ventricosa). 

Three thousand miles to the west, and in the same year as 
Locard, Verrill & Bush (1898) described what they thought to 



14 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



be Y. lucida from the North West Atlantic and two closely 
related north-east Atlantic species (Yoldiella iris and Yoldi- 
ella inflata). 

We have examined material from the Zoological Museum, 
Copenhagen, specimens identified by Verrill & Bush, the 
Jeffreys collections in London and Washington and Scandinavian 
material from a variety of sources which includes specimens 
identified by Dr. Kurt Ockelmann in his study of Greenland 
material. To prevent even more confusion we accept as our 
baseline that specimens from Eastern Arctic and northern 
temperate shallow water populations of the east Atlantic adja- 
cent to the type locality and which are described in the earliest 
accounts, as Yoldiella lucida s.s. We have also examined West 
Atlantic material some of which was misidentified and which we 
recognize as Y. lucida s.s. namely:- 

MCZ No. 137266 labelled Yoldiella inflata, S. Block 
Island, 180- 190 m. 

MCZ No. 227737 labelled Yoldiella lucida V & B, off 
Bradlees Bank, 120 m. 

MCZ No. 159722 (unlabelled). 

MCZ No. 202847 (which includes specimens from a num- 
ber of Stations mixed together). 

MCZ No. 78292 labelled Sta. 2697, off Halifax N.S., 377 
m. 

USNM No. 73172 labelled Y. lucida, 200 m. 

USNM No. 202847 labelled Gulf of Maine. Mixture from 
several stations. 

Specimens misidentified as Y. iris in the U.S. National 
Museum, but which are clearly Y. lucida s.s. :- 

USNM No. 74517 labelled Gulf of Maine, 172 m. 
USNM No. 159717 labelled Gulf of Maine, 40m. 
USNM No. 159718 labelled Gulf of Maine, 134 m. 

Samples of Y. lucida from the Skaggerak, loaned by the 
University Museum, Copenhagen, agree well with the figure 
of Sars (1878) and which Locard (1898) considered as the 
type (Fig. 1). These are also very similar to the shallow water, 
North American specimens referred to as Y. lucida and Y. iris 
by Verrill & Bush (1898). These latter specimens are very 
slightly more inflated but otherwise identical to the specimens 
taken from North American Basin Stations 105 and 207 (Figs. 
4&7). 

Thus, Y. lucida s.s. is found in Arctic and North Atlantic 
waters at shelf and upper slope depths, including the northern 
part of North America Basin, off Nova Scotia, Norwegian 
Sea, Greenland, Iceland, Skagerak and West European 
Basin. Depth range: 38-811 metres. 

Shell description (Figs. l-A & 15, Table 1). Shell elon- 
gate, ovate, moderately inflated, inequilateral, irregular con- 
centric ridges, partially opaque, umbos moderately large, 
inwardly directed, proximal dorsal margin close to umbos 
depressed in many but not all specimens, antero-dorsal and 
postero-dorsal margins raised to form sharp, low, keel on 
either side of umbo, distally antero-dorsal margin extends in 
almost straight line to point opposite anterior limit of hinge 
plate then curves to the anterior margin, ventral margin long, 
even curve, distal postero-dorsal margin slopes in almost 
straight line, close to dorsal limit of posterior margin maybe 
slightly upturned, limit of posterior margin supramedial, 
slightly truncate, postero-ventral margin not sinuous, but 
may be slightly flattened; hinge plate moderately broad, 




Fig. 2 Yoldiella lucida. Lateral views of shells from off the 
northeast coast of America; a, USNM No. 73172, 200 m; b, 
USNM No. 74517 labelled Yoldiella iris. Gulf of Maine, 172 m; 
USNM No. 159717 labelled Yoldiella iris, 40 m. (Scale = 1.0 
mm). 



c, 



except where narrow below umbo, anterior plate elongate 
extends opposite anterior margin of adductor muscle, poste- 
rior plate relatively short, does not reach posterior margin of 
posterior adductor muscle, hinge teeth chevron-shaped, mod- 
erately stout, maximum of 14 recorded in each series, occa- 
sionally anterior series has one more tooth than posterior; 
ligament amphidetic, moderately elongate, anterior and pos- 
terior lobes extend ventral to hinge plate. 
The above description is of a fully grown animal. In smaller 




Fig. 3 Yoldiella lucida. Outline drawings of shells from the right 
side from Sta. 105 to show change in shape with increase in size. 
(Scale = 1.0 mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



15 




Fig. 4 Yoldiella lucida. Hinge plates of a, right valve of a specimen from Sta. 105 (North America Basin); b & c, right and left valve of 
specimens from Thor' Sta. 28 to show variation in the shape of the ligament. (Scales = 0.5 mm). 



specimens the antero-dorsal margin is more convex, the 
postero-dorsal margin is normally angulate and the posterior 
margin more rounded (Fig. 4). As in many species of 
Yoldiella older specimens tend to become subrostrate. 

Prodissoconch length: 198 |xm. Maximum recorded shell 
length: 6.9 mm. 

Internal morphology. (Figs. 5 & 6) The mantle margin 
has a well-developed anterior sense organ. Posteriorly the 
siphons are combined, the inhalent siphon being open ven- 
trally. A well-developed feeding aperture lies immediately 
ventral to the siphons with numerous gland cells present in 
what is a broadened region of the inner muscular lobe. A long 
siphonal tentacle originates usually on the left side of the 
siphonal embayment near the base of the siphon. The adduc- 
tor muscles are large and unequal in size. The posterior 
muscle is oval in cross-section and between 1/2 and 1/3 the 
size of the anterior which is more circular in section. 

The visceral and cerebral ganglia are relatively large, 
club-shaped, with an exceptionally thick connecting commis- 
sure. The pedal ganglia are also large but more round in 
outline, and each with a large statocyst dorsal to it. The foot 
is anteriorly directed with well-developed pedal retractor 
muscles. The byssal gland is moderate in size. The gills are 
well-developed with between 16-23 gill filaments, the num- 
ber depending on the size of the individual. Posteriorly the 
gill axes attach to the junction between the two siphons. The 



labial palps are moderately large extending approximately a 
third across the body with between 13-23 palp ridges on the 
inner face. The palp proboscides are well-developed and are 
long and muscular. A wide ciliated oesophagus opens into a 
large stomach, the dorsal hood of which lies close to the 
dorsal margin of the body. There is a large style sac which 
penetrates the lower posterior half of the foot. The hind gut 
forms a single loop on the right side of the body. It has a 
typhlosole along its entire length. There are two digestive 
diverticula to the left and one on the right of the stomach. 
Material similar to that present in the stomach was observed 
in the left hand digestive diverticulum. The kidney is rela- 
tively small in comparison with Yoldiella species from deeper 
waters. The sexes are separate, and the gonads overlie the 
viscera dorsally and laterally. 203 ova were present in a 
specimen of 3.4 mm total length. 

Yoldiella obesa obesa (Stimpson 1851) 

Type locality. Original not known; Type locality here 
designated, St. Georges Bank, U.S. Fish Comm. Sta. 2072, 
2.10.1883, 43°53'N, 65°35'W, Beam Trawl, 858 fms. 

Type specimen. Holotype believed lost in Chicago fire. 
Neotype here selected, USNM No. 38419. 

Leda obesa Stimpson 1851, p. 113; Stimpson 1851, p. 10, pt. 
II, Fig. 1; Tryon 1873, p. 184, pi. 38, Figs. 500, 501. 



16 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 5 Yoldiella lucida. Lateral view of the internal morphology from the right side with detail of the posterior part of the mantle cavity and 
the partially expanded siphon. (Scales = 0.5 mm). 



Yoldia obesa Gould 1870, p. 155, Fig. 463; Verrill 1874, p. 46, 
p. 412, p.503; Smith & Harger 1874, p. 18, p. 23; 




Fig. 6 Yoldiella lucida. External view of the stomach as seen from 
a, antero-frontal; b, right lateral; c, left lateral aspects. (Scale = 
0.5 mm). 



Verrill 1874, p. 352, p. 368; Verrill 1874, p. 396. 
Yoldia lucida Verrill 1881, pi. XLIV, Fig. 1; Verrill 1884, p. 279 

(in part); Verrill 1885, p. 576 (in part); Bush 1893, p. 233. 
Yoldiella lucida Verrill & Bush 1897, p. 55. Fig. 14; Verrill & 

Bush 1898, p. 861, 862, 863, pi. 77, Fig. 2, pi. 80, Fig. 3. 
Yoldiella inflata Verrill & Bush 1897. p. 56. Figs. 3, 4. 11; 

Verrill & Bush 1898, p. 864, 865, pi. 80, Fig. 8, pi. 82, Fig. 

5,6. 



Material. 



Cruise 


Sta 


Depth 


No 


Lat 


Long 


Gear Date 






(m) 












NORTH AMERICAN BASIN 










Atlantis II 


62 


2496 


6 


36°26.0'N 


70°33.0"W 


ET 


21. 8.64 


12 


64 


2886 


8 


38°46.0'N 


70°06.0'W 


ES 


21. 8.64 




72 


2864 


11 


38°16.0'N 


71°47.0'W 


ES 


24. 8.64 


Chain 58 


103 


2033 


28 


39°43.6'N 


70°37.4'W 


ET 


4. 5.66 


Atlantis II 


128 


1254 


11 


39°46.5'N 


70°45.2'W 


ES 


16.12.66 


30 


131 


2178 


51 


39°38.5'N 
39°39.0'N 


70°36.5'W 
70°37.0'W 


ES 


18.12.66 


Chain88 


210 


2024- 


11 


39°43.0'N 


70°46.0'W 


ES 


22/ 






2064 




39°43.2'N 


70°49.5'W 




23. 2.69 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



17 



50 



30 
80 



W/L 



..• V % . 



60 



H/L 



• • * • • • •• 

• • • • ••• • •» 






60 



50 



PL/TL 



':\ 



.°- * 



— I - 

7 



Length (mm) 



Fig. 7 Yoldietla lucida. Comparison of the shell proportions of three populations; small closed circles, Gulf of Maine USNM 202847; large 
closed circles, a subsample from Thor' Sta. 28; open circles, a subsample from Sta. 105. H/L height/length, PL/TL postero-umbonal 
length/total length, W/L width/length - all against length. 

Also examined: 

U.S. Fish Comm. USNM 73163 labelled Y. lucida (Loven), 
Cisco Bay 1873 m; Station 2072 USNM 38419 labelled 
Yoldiella inflata (young), off Georges Bank 1569 m; 
USNM 35189 labelled Yoldiella inflata off Georges Bank 
2360 m. 

Restricted to the North American Basin at lower slope 
depths. Depth range 1254-2886 metres. 

Shell description (Figs. 8-9 & 15). Shell moderately frag- 
ile, elongate, ovate, with fine concentric ridges, inequilateral; 
umbo moderately inflated, anterior, inwardly directed; dorsal 
margin in the region of the umbos in all but a few specimens, 
slightly concave, dorsal margins form sharp raised edge, 
antero-dorsal margin smooth curve joining anterior margin 
with no angulation, ventral margin smooth, relatively deep 
curve, postero-dorsal margin in large specimens almost 
straight, subangulate with posterior margin, extreme poste- 
rior limit of shell dorsal to horizontal midline; hinge plate 
moderately strong, parallel to margin, chevron-shaped teeth 
fairly stout, anterior and posterior hinge plates with same 
number of teeth, occasionally with one additional tooth on 
posterior plate; ligament amphidetic, circular in lateral view, 
extends ventral to hinge plate but without chondrophore, 
short anterior and posterior secondary external periostracal 
extensions. 

Prodissoconch length: 215 urn. Maximum recorded shell 
length: 4.45 mm. 




Fig. 8 Yoldiella obesa obesa. Neotype: USNM No. 38419. Lateral 
view of a right valve and a hinge plate of left valve, also a dorsal 
view of the umbos showing the outline of the prodissoconch. 
(Scale = 1.0 mm). 



18 J.A. ALLEN, H.L. SANDERS AND F. HANNAH 

Table 1 Yoldiella lucida; numbers of anterior and posterior hinge teeth in specimens from different localities. 





Biscay 






North Atlantic 






Thor' N. 


European 






Length 


Teeth 


No. 


USNM. 


Length 


Teeth 


No. 


Length 


Teeth 


No. 




(mm) 


Ant. 


Post. 


No. 


(mm) 


Ant. 


Post 


(mm) 


Ant. 


Post. 


INCAL DS 02 


2.28 


6 


6 


738419 


3.07 


8 


8 


2.50 


8 


7 


INCAL DS 01 


2.42 


7 


7 


159718 


3.22 


10 


10 


2.77 


8 


9 


INCAL DS 01 


2.75 


7 


7 


74517 


3.35 


11 


10 


2.91 


9 


9 


INCAL DS 01 


2.95 


8 


8 


202847 


3.84 


11 


11 


3.44 


9 


9 


INCAL CP 01 


3.24 


9 


9 


202847 


3.94 


11 


11 


3.49 


9 


10 


INCAL DS 01 


3.28 


8 


8 


202847 


4.03 


11 


10 


4.31 


11 


11 


INCAL CP 01 


3.49 


8 


8 


202847 


4.51 


12 


12 


4.39 


12 


12 


INCAL DS 02 


3.57 


9 


9 


202847 


4.67 


11 


11 


4.67 


11 


11 


POLYGAS 






















DS26 


3.61 


11 


11 


73172 


4.93 


12 


12 


5.02 


11 


12 


INCAL DS 01 


3.77 


10 


10 


202847 


5.98 


12 


14 


5.02 


14 


14 


INCAL DS 01 


4.31 


10 


10 


202847 


6.02 


15 


14 


5.10 
5.10 
5.10 
5.10 
5.19 
5.61 


13 
11 
11 
13 
12 
13 


14 
12 
12 
13 
11 
13 



Very similar to Y. lucida (for points of difference see 
p. 19), past records e.g. (Verrill & Bush, 1898; Waren, 1989) 
testify to this. 

Internal morphology (Fig. 10). The internal morphology 
is similar to that of Y. lucida. There is a well-developed 
ciliated anterior mantle sense organ. The inhalent and exhal- 
ent siphons are combined for most of their length, and the 
inhalent siphon is not fused along its ventral margin. The 
siphonal tentacle is well-developed and usually attached to 
the left of the base of the siphons. The feeding aperture is 




Fig. 9 Yoldiella obesa obesa. Lateral views of shells from the right 
side to show change in shape with increasing size and detail of 
hinge plate. Specimens from Sta. 62 North America Basin. Note 
adductor muscles and hind gut loop seen through the transparent 
shell. (Scale =1.0 mm). 



also well-developed and provided with numerous gland cells. 
The broad and, in preserved specimens, convoluted part of 
the inner muscular lobe which forms the feeding aperture, 
extends anteriorly beyond the limit of the aperture and is 





Fig. 10 Yoldiella obesa obesa. Lateral views of the internal 
morphology from right and left side. (Scale =1.0 mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



19 



heavily ciliated throughout. The adductor muscles are rela- 
tively large and unequal in size. The posterior muscle is oval 
in outline and is approximately 1/2 to 1/3 the size of the 
anterior muscle. 

The gills are well-developed with up to 16 gill filaments 
depending on the size of the individual. The number of ridges 
on the inner surface of the labial palp varies between 12-17. 
The palps extend over approximately half the body width and 
have long, moderately thick palp proboscides. The visceral 
and cerebral ganglia are elongate and each large pedal 
ganglia has a large statocyst dorsal to it. The foot is large and 
directed anteriorly, with well-developed retractor muscles. 
There is a moderately large byssal gland in the heel. The 
oesphagus is wide and opens into a voluminous stomach. The 
style sac penetrates into the lower portion of the foot. The 
hind gut forms a single loop on the right side of the body and 
has a typhlosole along its entire length. The digestive diver- 
ticula, as in other species, are situated one to the right and 
two to the left of the stomach. The ducts to the left hand 
diverticula enter the stomach close together, ventral to the 
gastric shield one posterior to the other. The kidney is small. 
Gonads overlie the lateral and dorsal sides of the viscera and 
the sexes are separate. 

Y. obesa s.s. and Y. lucida differ as follows:- (1) The 
ventral margin of Y. obesa is slightly deeper and more 
rounded. (2) The anterior adductor of Y. obesa is relatively 
smaller when compared with a specimen of Y. lucida the 
same size. (3) The internal ligament of Y. obesa is smaller, 
shorter and more rounded. (4) The umbo is more anterior in 
Y. obesa and slightly larger and more prominent. (5) The 
posterior margin is more rostrate and tapered in Y. obesa and 



Fig. 11 Yoldiella obesa incala. Lateral view of shells from the right 
side to show change in shape with increasing size, and detail of 
the hinge plate of a right valve. Specimens from Incal Sta. DS02. 
(Scales =1.0 mm). 



less truncate. (6) The posterior section of the loop of the hind 
gut is less curved and almost vertical in Y. obesa. 

Yoldiella obesa incala (new subspecies) 

Type locality. R.V. Jean Charcot, Cruise INCAL, Sta. 
DS01, East of Rockall Island, 15.7.1976, 57°59'N, 10°40'W, 
Epibenthic Trawl, 2091 m. 

Type specimen. Holotype: Museum National d'Histoire 
Naturelle, Paris, Paratypes: in collection held by J. A. Allen. 

Material. 



Cruise 


Sta Depth 


No 


Lat 


Long 


Gear Date 




(m) 












WEST EUROPEAN BASIN 










Jean Charcot DS25 2096 


3 


44°08.2'N 


4°15.7'W 


DS 


1.11.71 


(Polygas) 


DS26 2076 


3 


44°08.2'N 


4°15.0'W 


DS 


1.11.71 


Jean Charcot DS51 2430 


1 


44°11.3'N 


4°15.4'W 


DS 


12. 2.74 


(Biogas IV) 














(Biogas V) 


CP07 2170 


4 


44°09.8'N 


4°16.4'W 


CP 


21. 6.74 


(Biogas VI) 


DS80 4120 


2 


46°29.5'N 


10°29.5'W 


DS 


27.10.74 




DS86 1950 


7 


44°04.8'N 


4°18.7'W 


DS 


31.10.74 




DS87 1913 


5 


44°05.2'N 


4°19.4'W 


DS 


1.11.74 


(Incal) 


DS01 2091 


518 


57°59.0'N 


10°40.0'W 


DS 


15. 7.76 




DS02 2081 


452 


57°58.0'N 


10°49.0'W 


DS 


16. 7.76 




CP01 2068- 


35 


57°57.0'N 


10°43.0'W 


CP 


16. 7.76 




2040 














CP02 2091 


3 


57°58.0'N 


10°43.0'W 


CP 


16. 7.76 




Restricted to the West European Basin at lower slope depths. 
Depth range: 1913-2170 mm. 

SHELL DESCRIPTION (Figs. 11 & 12). Y. obesa incala is similar 
to Y. obesa s.s. and requires little description other than to 
identify points of differences with the North American sub- 
species. 



50 



W/L 



30 J 
80 



60 
6& 



H/L 






PL/TL 



12 3' 

Length (mm) 

Fig. 12 Yoldiella obesa incala. Variation in the ratios of height 
H/L, width W/L and postero-umbonal length PL/TL to length 
against length of a sample from Incal Sta. CP01 from the Bay of 
Biscay. 



20 

The subspecies has been long confused with Y. lucida s.s. 
(Waren, 1989) and there is little doubt that records of the 
latter species from deeper than 1000 m are of Y. obesa incala. 
In large specimens in particular, elongation and narrowing of 
the posterior margin together with a slightly upturned distal 
end of the postero-dorsal margin, resembles Y. lucida. A 
population from Rockall although similar in outline is rela- 
tively smaller and less inflated than the Biscay populations. 

Prodissoconch length: 187-208 |xm. Maximum recorded 
shell length: 4.8 mm. 

Internal morphology. Mantle structures are similar to 
those in Y. obesa s.s., for example the ventral margin of the 
inhalent siphon is open ventrally, however the feeding aper- 
ture is not particularly well-developed. The posterior adduc- 
tor muscle is oval in shape and half the size of the crescent- 
shaped anterior muscle. There is a large stomach and style 
sac, and a single loop of the hind gut on the right side of the 
body. The byssus gland is moderately small. The palp probos- 
cides are long and palp ridges number up to 21. The gills are 
well-developed with up to 17 plates present. 

Points of distinction are as follows:- (1) The umbo in Y. 
obesa incala is slightly more medial than in Y. obesa s.s. (2) 
The posterior dorsal section of the hind gut loop takes a 
slightly more anterior course than in Y. obesa s.s. (3) The 
anterior adductor is relatively more ventral in position than in 
Y. obesa s.s. (4) Although the ligament is relatively short 
and, in many specimens rounded as it is in the North 
American subspecies, in some specimens the anterior and 
posterior ends are slightly swollen giving a 'dumb bell' 
appearance. 

In a specimen 3.03 mm length, 281 ova were counted, with 
a maximum diameter 119 |xm. In two specimens less mature, 
240 and 387 ova were present in animals measuring 3.06 mm 
and 4.23 mm respectively. 




J. A. ALLEN, H.L. SANDERS AND F. HANNAH 

Yoldiella similiris (new species) 

Type locality. R.V. Atlantis II, Cruise 60. Sta. 236, 
Argentine Basin, 11.3.1971, 36°27.0'S, 53°31.0'W-36°28.1'S, 
53°32.3'W, Epibenthic Trawl, 409-518 m. 

Type specimen. Holotype: BM(NH) 1992028. Paratypes: in 
collection held by J. A. Allen. 

Material. 



Cruise Sta Depth 
(m) 


No 


Lat 


Long 


Gear Date 


ARGENTINE BASIN 










Atlantis II 236 409- 
60 518 
237 993- 
1011 


86 
5 


36°27.0'S 

-36 28.1'S 

36°32.6'S 


53°31.0'W 
53°32.3'W 
53°23.0'W 


ES 11.3.71 
ES 11.3.71 



Restricted to shallow slope depths in the Argentine Basin. 
Depth range: 497-1011 metres. 

Shell description (Figs. 13, 15-17). Shell small, subovate, 
moderately inflated, smooth, fine irregular concentric lines, 
inequilateral; umbos small, anterior of midline, inwardly 
directed; antero-dorsal margin convex, curves evenly to ante- 
rior margin, ventral margin convexity increases slightly poste- 
riorly, posterior margin obliquely subtruncate, postero-dorsal 
margin approximately straight, gently sloping, posteriorly 
forming a blunt angle, dorsal margins on either side of umbo 
form an acute edge; hinge plate well-developed, anterior 
slightly arched, posterior almost straight, 11 anterior and 12 
posterior strong angular teeth in individual 3.75 mm long; 
ligament amphidetic, small secondary external periostracal 
extensions on either side of umbo, internal primary ligament 
moderately large, extends below hinge line. 

Prodissoconch length: 198 u.m. Maximum recorded shell 
length: 3.75 mm. 

The shell and internal morphology of Y. similiris is very 
similar to that of Y. lucida s.s. The following differences are 
noted:- The umbo of Y. similiris is slightly more anterior, this 




Fig. 13 Yoldiella similirus. Lateral views of shells from the right 
side and a hinge plate of a left valve. Specimens from Sta. 236 
Argentine Basin. (Scale = 1.0 mm). 



Fig. 14 Yoldiella similiris. Lateral view of internal morphology 
from the right side. (Scale =1.0 mm). For identification of parts 
see Fig. 5. 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



21 







Fig. 16 Yoldiella similiris. Lateral views of a series of shells to 
show changes in shape with growth. Specimens from Sta. 236 
Argentine Basin. (Scale = 1.0 mm). 




Fig. 15 Yoldiella spp. Dorsal 
views of shells of a, Y. obesa 
Q obesa; b, Y. similiris and c, Y. 

lucida. (Scale = 1.0 mm). 

is particularly noticeable in the larger specimens. The height 
to length ratio is greater in Y. similiris. 

Internal morphology (Fig. 14). The internal morphology 
is very similar to that of Y. lucida. The adductor muscles are 
unequal in size, the posterior muscle is oval and approxi- 
mately 1/3 the size of the anterior. There are a smaller 
number of gill filaments (maximum of 11 observed) and the 
labial palp ridges vary between 11-13. The stomach and style 
sac appear relatively smaller than those in Y. lucida and the 
hind gut, while making a single loop on the right side of the 
body, is not as deep as it is in the latter species. A maturing 
female (3.4 mm total length) had 203 ova with a maximum 



50i 



30 
80 



W/L 



H/L 



60 
60 
50H 



PL/TL 



12 3 4 

Length (mm) 

Fig. 17 Yoldiella similiris. Variation in the ratios of height H/L, 
width W/L and postero-umbonal length to length against length of 
a subsample from Sta. 236. Argentine Basin. 



22 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



diameter of 83 |xm (probably less than half their eventual 
maximum size). 

Yoldiella hanna (new species) 

Type locality. R.V. Atlantis II Cruise 42, Sta. 186, Cape 
Basin, 15.5.1968, 22°57'S, 13°05'E, Epibenthic Trawl, 
439-481 m. 

Type specimen. Holotype BM(NH) 1992022, Paratypes: in 
collection held by J.A. Allen. 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



CAPE BASIN 

Atlantis II 186 439- 21 22°57.0'S 13°05.0'E ES 16.5.68 
42 481 

188 619- 7 23°00.0'S 12°58.0'E ES 16.5.68 
622 

The species is restricted to the upper slope in the Cape Basin. 
Depth range: 439-622 metres. 

Shell description (Fig. 18). Shell small, ovate, relatively 
inflated, inequilateral (posterior umbonal length 52-57% of the 
total length), sculpture, fine concentric lines at ventral margin, 
pale straw-coloured periostracum; umbos slightly raised, 
inwardly directed; dorsal margin slightly convex, antero-dorsal 




Fig. 18 Yoldiella hanna. Lateral views from the right side of three 
shells and an internal view of a right valve to show detail of the 
hinge plate. Specimens from Sta. 186 Cape Basin. (Scale = 1.0 
mm). 




Fig. 19 Yoldiella hanna. Lateral view from right side of the 
internal morphology. Specimen from Sta. 186 Cape Basin. (Scale 
= 1.0 mm). For identification of parts see Fig. 5. 

margin slopes gradually and smoothly to anterior margin, dorsal 
part of which more convex, ventral margin long, smooth, curve, 
postero-dorsal margin almost straight maybe slightly concave, 
slopes gently to blunt-angled supramedial posterior margin; 
hinge plate very strong, wide, except centrally under umbo; 10 
strong chevron-shaped teeth on each side of ligament in largest 
specimen; ligament amphidetic, goblet-shaped, extends below 
margin of hinge plate. 

Prodissoconch length: 200 |xm. Maximum recorded shell 
length: 3.2 mm. 

Internal morphology (Fig. 19). Well-developed combined 
siphons are present with a well-developed feeding aperture 
ventral to them. The siphonal tentacle lies to the left. The 
posterior adductor muscle is very small and elongate oval in 
cross-section. The anterior adductor muscle is crescent-shaped 

6C h 

• _ • • • 

-W/L 

o o 

o 
40-- 

80- 



H/L 



60-- 

60- 

50-- 






PL/TL 



Length (mm) 



Fig. 20 Yoldiella spp. Comparison of the shell proportions of Y. 
hanna (closed circles) and Y. artipica (open circles). Height H/L, 
width W/L and postero-umbonal length PL/TL to length against 
length. 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



23 



and at least three times as large as the posterior. The foot is 
large, anteriorly directed and with a large byssal gland. The 
cerebral and visceral ganglia are relatively large, club-shaped 
with a stout commissure. The pedal ganglia are also large but 
more rounded. The labial palps are well-developed and extend 
across approximately half of the body and have up to 14 broad 
internal ridges present on their inner face. The palp proboscides 
are moderately long. The gills are small with up to 18 alternating 
filaments. 

The stomach is large and laterally distended. The proximal 
part of the hind gut penetrates deep into the foot, ventral to 
the pedal ganglia. It forms a single loop on the right side of 
the body. 

In external appearance the shells of the species can be 
easily confused with Yoldiella artipica (p. 25) although Y. 
hanna is slightly more inflated and the height/length ratio is 
slightly greater (Fig. 20). Nevertheless, hinge and teeth differ 
markedly, as does the hind gut configuration. 

Yoldiella capensis (new species) 

Type locality. R.V. Atlantis II, Cruise 42, Sta. 189, Cape 
Basin, 15.5.1968, 23°00'S, 12°45'E, Epibenthic Trawl, 
1007-1014 m. 

Type specimen. Holotype BM(NH) 1992026, Paratypes: in 
collection held by J. A. Allen. 

Material. 



Cruise Sta 


Depth 

(m) 


No 


Lat 


Long 


Gear Date 


CAPE BASIN 












Atlantis II 188 


619- 


70 


23°00.0'S 


12°58.0'E 


ES 16.5.68 


42 


622 










189 


1007- 
1014 


918 


23°00.0'S 


12°45.0'E 


ES 15.5.68 


190 


974- 
979 


15 


23°05.0'S 


12°45.0'E 


AD 17.5.68 



Only found at slope depths of the Cape Basin. Depth range: 
619-1014 m. 

Shell description (Figs. 21 & 22). Shell, subovate, moder- 
ately inflated, inequilateral, posteriorly somewhat wedge- 
shaped, smooth with a few fine concentric lines, periostracum 
pale straw-coloured; umbos slightly raised, inwardly directed; 
antero-dorsal margin convex, slopes steeply from umbo to 
anterior margin, dorsally posterior margin produced into 
rounded point, postero-dorsal margin long, varying from 
slightly convex in smaller specimens (usually) to slightly 
concave, slopes gradually to posterior margin, hinge plate 
strong, relatively long, plates approach shell margin below 
umbo, anterior plate arched with up to 9 erect chevron teeth, 
posterior plate extends to anterior margin of adductor, 
straighter than anterior, with up to 11 teeth and does not 
1 extend beyond posterior margin of adductor; ligament 
amphidetic, bilobed in lateral view, extends below hinge line. 

Prodissoconch length: 170 \x.m. Maximum recorded shell 
length: 8.0 mm. 

With increasing size this species becomes more posteriorly 
elongate and the distal posterior dorsal limit more pointed 
(Figs. 21 & 22). Furthermore the posterior dorsal margin 
becomes less curved with increasing size, so much so that 




Fig. 21 Yoldiella capensis. Lateral view from the left side of the 
largest shell taken from Sta. 189 Cape Basin and hinge detail of 
right valve of the same specimen. (Scale = 1.0 mm). 




Fig. 22 Yoldiella capensis. Lateral views of shells from the right 
side to show change in shape with growth. Specimens from Sta. 
188 Cape Basin. (Scale =1.0 mm). 

without a size series it would be difficult to equate small 
specimens with large. Other shell ratios (H/L and W/L) 
remain more or less constant as length increases (Fig. 23). 

Internal morphology (Fig. 24). Specialization of the 
mantle includes a well-developed anterior sense organ and 
combined exhalent and inhalent siphons. The latter are 
well-developed with thick muscular walls. A siphonal tentacle 
lies to the left of the siphons. There is a feeding aperture 
ventral to the siphons which is much folded in the contracted 
state. The adductor muscles are relatively small. The poste- 
rior muscle is narrow and elongate, while the anterior is 2 to 3 
times larger and crescent-shaped. 

The gills are well-developed with up to 20 plates. The labial 
palps are moderate in size. They extend between 1/4 - 1/3 
distance across the body and have long and slender palp 
proboscides. The nervous system is well developed with large 
club-shaped visceral and cerebral ganglia and massive com- 
missures which link them. Large, round, pedal ganglia each 
have a large statocyst full of retractile granules dorsal to 



24 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



50 



30 

80 



W/L 



H/L 



60 
60 
50H 



PL/TL 



1 2 3 

Length (mm) 

Fig. 23 Yoldiella capensis. Variation in the ratios of height H/L, 
width W/L, and postero-umbonal length PL/TL to length against 
length of a subsample of specimens from Sta. 188 Cape Basin. 




Fig. 24 Yoldiella capensis. Lateral view from the right side of the 
internal morphology. Specimen from Sta. 188, Cape Basin. (Scale 
= 1.0 mm). For identification of the parts see Fig. 5. 

them. The foot is large, well-developed with an anteriorly 
directed attitude. The stomach and style sac are also large. 
The hind gut forms a single loop on the right side of the body. 
This species bears some resemblance to Yoldiella lucida and 
to Y. bilanta (Fig. 137). 



Yoldiella bilanta (new species) 

Type locality. R.V. Atlantis II, Cruise 42, Sta. 192, Cape 
Basin, 17.5.1968, 23°05.0'S, 12°31.5'E, Epibenthic Trawl, 
2117-2154 m. 



Type specimen. Holotype: BM(NH) 1992027, Paratypes: in 
collection held by J.A. Allen. 

Material. 



Cruise 



Sta 



Depth No 
(m) 



Lat 



Long 



Gear Date 



CAPE VERDE BASIN 

Atlantis II 138 1944- 1 10°36.0'N 17°52.0"W ES 4.2.67 
31 1976 

141 2131 2 10°30.0'N 17°51.5'W ES 5.2.67 

142 1624- 1 10°32.0'N 17°51.5'W ES 5.2.67 
1796 

144 2051- 22 10°36.0'N 17°49.0'W ES 5.2.67 
2357 

CAPE BASIN 

Atlantis II 191 1546- 1025 23°05.3'S 12°31.5'E ES 17.5.68 
42 1559 

192 2117- 1697 23°02.0'S 12°19.0'E ES 17.5.68 
2154 

Found in the Cape Verde and Cape Basins at lower slope 
depths. Depth range: 1446-2357 metres. 

Shell description (Fig. 25). Shell slender, elongate ovate, 
inequilateral, smooth with few fine concentric lines, perios- 
tracum pale straw-coloured; umbos anterior to midline, 
slightly inflated, orthogyrate; antero-dorsal margin moderat- 
ley convex, curves evenly to anterior margin, ventral margin 
long, smooth curve, anterior curvature slightly more convex 
than posterior, posterior margin narrow, slightly produced 
with supramedial rounded angle, postero-dorsal margin 
slopes gradually more or less straight or slightly concave from 
umbo to posterior limit of hinge plate, then more acutely to 
posterior margin; hinge plate, strong, long, relatively narrow 
and straight with 9 anterior and 10 posterior teeth in largest 
specimen; anterior and posterior plates approach margin 
below umbo; ligament amphidetic, bilobed goblet-shaped, 
extends below hinge line, short anterior and posterior exter- 
nal extensions of fused periostracum. 

Prodissoconch length c 190 p.m: Maximum recorded shell 
length: 8.0 mm. 

The morphology of the shell is similar to that of Yoldiella 
capensis (Fig. 21). With increasing size the shell becomes 
more posteriorly elongate and the postero-dorsal margin 
becomes more straight so that the slight angulation at the 
level of the limit of the posterior hinge margin becomes much 
less obvious (Figs. 25 & 26). There is little change with 
growth in the height and length and width to length ratios. 
The hinge plate is more narrow and teeth less robust than in 
Y. capensis and the lateral 'dumb bell' outline of the ligament 
is very different from the more rectangular and deeper 
ligament of the latter species. 

Internal morphology (Fig. 27). The most conspicuous 
difference from Y. capensis is the size and shape of the 
adductor muscles which are larger and more rounded in 
Yoldiella bilanta The labial palps are relatively small and 
extend approximately 1/3 distance across body. They bear up 
to 16 palp ridges. The gill plates are relatively narrow and 
number up to 18. The single loop of the hind gut has a greater 
diameter but is not as ventrally deep as that in Yoldiella 
capensis. Similar features to Yoldiella capensis include well- 
developed combined siphons, nervous system, and a large, 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



25 




Fig. 25 Yoldiella bilanta. Lateral views 
of three shells from the right side and 
internal view of a left valve to show the 
hinge-plate. Specimens from Sta. 192 
Cape Basin. (Scale = 1.0 mm). 



50 



W/L 



•; ••»*. 



30 J 
80 



60 
60 
50 



H/L 



PL/TL 



Length(mm) 



Fig. 26 Yoldiella bilanta. Variation in 
the ratios of height H/L, width W/L, 
and postero-umbonal length PL/TL to 
length against length of samples from 
Sta. 191 (open triangles) and Sta. 192 
(closed circles) Cape Basin. 



anteriorly directed foot. The lateral papillae of the foot are 
not so well-developed as those in Y. capensis. 

The specimens from the Cape Verde Basin are somewhat 
smaller and have a slightly deeper shell than those from the 
Cape Basin. There appear also slight differences in the size of 
the posterior adductor muscle and the gills, but these may be 
a result of distortion following preservation. Such small 
differences are within the normal variation of yoldiellid 
species and at most represent a population difference. 



Yoldiella artipica (new species) 

Type locality. R.V. Atlantis II, Cruise 42, Sta. 200, 
Angola Basin, 22.5.1968, 9°43.5'S, 10°57'0E - 9°41.0'S - 
10°55.0'E, Epibenthic Dredge, 2644-2754 m. 



Type specimen. : Holotype: BM(NH) 1992021, Paratypes: 
in collection held by J. A. Allen. 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



ANGOLA BASIN 

Atlantis II 200 2644- 25 9°43.5'S 

42 2754 - 9°41.0'S 

Walda DS20 2514 2 2°32.0'S 



10°57.0'E ES 22.5.68 

10°55.0'E 

8°18.1'E ES -.-.71 



Restricted to the abyssal rise of the south east Atlantic. 
Depth range: 2514-2754 m. 



26 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 27 Yoldiella bilanta. Lateral view of the internal morphology 
from the right side of a specimen from Sta. 192 Cape Basin. 
(Scale 1.0 mm). For identification of parts see Fig. 5. 

Shell description (Fig. 28). Shell small, ovate, not 
inflated, inequilateral (posterior umbonal length 54-58% of 
total length), in larger specimens antero-ventrally, very fine 
concentric lines form broadly spaced ridges, periostracum 
pale yellow, umbo slightly raised, inwardly directed; dorsal 
margin slightly convex, antero-dorsal margin curves moder- 
ately steeply and evenly with anterior margin, ventral margin 
smooth curve, postero-dorsal margin slopes gently from 
umbo to extended posterior margin; ligament amphidetic, 
small, rounded, not extending below hinge plate, with small 
secondary anterior and posterior external extensions of fused 
periostracum ; hinge plate moderately long, relatively nar- 
row, small chevron-shaped teeth, 7 anterior and 8 posterior. 

Prodissoconch length: 200 |xm. Maximum recorded shell 
length: 2.78 mm. 

Shell measurements (mm) & ratios are as follows:- 



Length 


Height 


Width 


H/L 


W/L 


PL/TL 


2.00 


1.46 




0.73 




0.54 


2.69 


1.89 


- 


0.70 


- 


0.56 


2.78 


1.98 


- 


0.71 


- 


0.58 


1.64 


1.13 


0.53 


0.69 


0.33 


0.54 


2.23 


1.55 


0.84 


0.70 


0.38 


0.57 


2.60 


1.80 


1.01 


0.69 


0.38 


0.55 


2.52 


1.76 


1.01 


0.70 


0.40 


0.57 



PL = postumbonal length 

Internal morphology (Fig. 29). The combined exhalent 
and inhalent siphons are large. The inhalent is somewhat 
shorter than the exhalent and open ventrally. A large sipho- 
nal tentacle originates on the left side of the siphonal embay- 
ment close to the base of the siphon. The feeding aperture is 
not particularly well-developed. There is a large anterior 
sense organ. The posterior adductor muscle is long and 
narrow, and only half the size of the bean-shaped anterior 
muscle. The gills are well-developed with up to 20 gill plates. 
The labial palps are relatively small with up to 12 internal 
palp ridges with long, thin palp proboscides. The foot is 
extremely long and slender with an extended sole fringed 
with deep papillae. There is a large byssal gland in the heel 
with large pedal ganglia dorsal to it. The visceral and cerebral 
ganglia are of moderate size and club-shaped. The hind gut is 
similar to that in Yoldiella lata (p. 32) with one complete turn 
of a double loop to the right side. That in Y. artipica entends 
further posteriorly than that in Y. lata. As in many yoldiellid 
species the body wall enclosing the hind gut loops overhangs 
the palps on the right side (Fig. 29). 



Yoldiella similis (new species) 

Type locality. R.V. Atlantis II, Cruise 42, Sta. 197, 
Angola Basin, 21.5.1968, 10°24'S, 9°09'E - 10°29'S, 9°04'E, 
Epibenthic Trawl, 4559-4566 m. 




Fig. 28 Yoldiella artipica. A dorsal and two right 
lateral views of shells, and one lateral view of a left 
valve to show detail of hinge-plate. Specimens from Sta. 
200 Angola Basin. (Scale =1.0 mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



27 





Fig. 29 Yoldiella artipica. Lateral view from the right side of the 
interal morphology of a specimen from Sta. 200 Angola Basin. 
(Scale = 1.0 mm). For identification of parts see Fig. 5. 

Type specimen. Holotype: BM(NH) 1992023, Paratypes: 
collection held by J. A. Allen. 

Material 



in 



Fig. 30 Yoldiella similis. Lateral view of a shell from right side and 
a hinge-plate of a left valve compared with the hinge-plate of a 
specimen of Y. jeffreysi (a) Specimens from Sta. 197, Angola 
Basin and Sta. 316, West European Basin, respectively. (Scale = 
1.0 mm). 



Shell measurements (mm) and ratios are as follows:- 



Cruise 



Sta 



Depth No 
(m) 



Lat 



Long 



Gear Date 



Length Height 



Width 



H/L 



W/L 



PL/TL 



ANGOLA BASIN 












1.0 


0.71 


0.78 


0.71 


0.38 


0.42 


Atlantis II 196 
42 

197 


4612- 1 
4630 
4596 35 


10°19.0'S 


9°04.0'E 


ES 


21.5.68 


1.93 

1.72 


1.39 
1.43 


0.80 
0.80 


0.72 
0.83 


0.41 
0.46 


0.50 
0.54 


10°29.0'S 


9°04.0'E 


ES 


21.5.68 


2.90 


2.06 


1.39 


0.71 


0.48 


0.55 


198 


4559- 12 


10°24.0'S 


9°09.0'E 


ES 


21.5.68 
















4566 


- 10°29.0'S 


9°04.0'E 






PL = 


postumbonal length 









Found at abyssal depths in the Angola Basin. Depth range: 
4559-4630 m. 

Shell description (Fig. 30). Shell small, ovate, very 
slightly inflated, inequilateral with posterior margin suprame- 
dially subrostrate, shell with very fine concentric lines, form- 
ing ridging on ventral half of shell; periostracum pale yellow; 
umbos slightly raised, internally directed; dorsal margin 
slightly convex, antero-dorsal margin slopes from umbo to 
form even curve with anterior margin, ventral margin 
smoothly curved, posterior margin sharply curved where it 
meets postero-dorsal margin; hinge strong, moderately 
broad, extends to anterior and posterior limits of the anterior 
and posterior adductors respectively; hinge teeth well- 
developed, equal numbers (maximum 9) on anterior and 
posterior hinge plates, ligament amphidetic, moderately 
large, goblet-shaped with very small external extensions. 

Prodissoconch length: 173 u.m. Maximum recorded shell 
length: 2.92 mm. 

The shell outline of this species is similar to that of 
specimens of Y. jeffreysi from the Cape Verde Basin. The two 
species can be distinguished by the larger ligament, broader 
hinge and more rostrate posterior margin of Y. similis. 



Internal morphology (Fig. 31). The internal morphology 
of Y. similis is very similar to that of Y. jeffreysi. The exhalent 
siphon is combined with the less well-developed inhalent 
siphon. The adductor muscles are unequal in size, the ante- 
rior being approximately three times larger than the poste- 
rior. In lateral view the posterior adductor muscle is oval in 
outline while the anterior is 'bean-shaped'. The foot has a 
long, extended, narrow sole with a large byssal gland in the 
heel. The nervous system is extremely well-developed with 
large visceral and cerebral ganglia with short stout commis- 
sures joining them. Gills appear to have relatively few plates 
(up to 10) and the number of palp ridges is also few (up to 12) 
but the latter are relatively broad. This species has a large 
stomach and the hind gut makes one complete double coil to 
the right side of the body. 



Yoldiella sinuosa (new species) 

Type locality. R.V. Knorr, Cruise 25, Sta. 299, Surinam 
Basin, 29.2.1972, 7°55.1'N, 55°42.0'W, Epibenthic Trawl, 
1942-2076 m. 



28 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 31 Yoldiella similis. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 197. Angola Basin. 
(Scale = 1.0 mm). For identification of parts see Fig. 5. 

Type specimen. Holotype: BM(NH) 1992025, Paratypes: in 
collection held by J. A. Allen. 

Material. 



Cruise 



Sta 



Depth No Lat 
(m) 



Long 



Gear Date 



SURINAM BASIN 



Knorr 25 



299 1942- 54 
2076 



7°55.1'N 55°42.0'W ES 29.2.72 



Restricted to one Station on the lower slope of the Surinam 
Basin. Depth range: 1942-2076 m. 

Shell description (Figs. 32 & 33). Shell small, ovate, 
moderately inflated, slightly inequilateral, surface smooth in 
small individuals, ridges on ventral half of shell of larger 
specimens, periostracum pale yellow; umbo small, slightly 
raised, internally directed; no lunule or escutcheon; dorsal 
margin convex, anterior and posterior margins slope at 
similar angle from umbo, anterior margin smooth curve, 
posterior margin slight extended and slightly subrostrate, 
postero-dorsal margin slightly angled at posterior limit of 
hinge plate, postero-ventral margin sinuous, ventral margin 
slightly more convex posteriorly; hinge plate strong, rela- 
tively long, with up to 9 anterior and 10 posterior chevron- 
shaped teeth, hinge plate narrow below umbo; ligament 
amphidetic, internal, 'goblet-shaped'. 

With increasing shell length, there is little change in the 
height to length ratio but there is a slight increase in the width 
to length ratio. There is also gradual post-umbonal extension 
with the sinuous nature of the postero-ventral margin becom- 
ing more conspicuous (Fig. 35). 

Prodissoconch length: 179 |xm. Maximum recorded shell 
length: 3.69 mm. 

Internal morphology (Fig. 34). The combined siphons, 
the siphonal tentacle (usually on the left side), and the 
anterior sense organ are as in Y. similis. The adductor 



Fig. 32 Yoldiella sinuosa. Lateral view of a shell from the right 
side and detail of the hinge-plate of a right valve. Specimens from 
Sta. 299 Guyana Basin. (Scale = 1.0 mm). 




Fig. 33 Yoldiella sinuosa. Outline drawings of shells of different 
sizes from the right side to show change in shape with growth. 
Specimens from Sta. 299 Guyana Basin. (Scale = 1.0 mm). 

muscles are approximately oval, the anterior muscle being 
the larger and being almost twice the size of the posterior. 
The gills have up to 17 plates. The labial palps are moderate 
in size and extend 1/3 way across the body. They have up to 
15 moderately broad ridges and each bears a long palp 
proboscis. The pedal ganglia are large, round, with large 
statocysts dorsal to them. The cerebral ganglia are slightly 
larger than the visceral, both are club-shaped and well- 
developed. The foot is large with a large byssal gland. The 
stomach is large with a small, narrow style sac. The hind gut 
takes an 'S-shape' course to the right side of the body before 
returning to the mid dorsal margin and thence to the anus. 
There is a fine typhlosole present along the length of the hind 
gut. Ingested material was seen in part of the left digestive 
diverticulum. The kidney is well-developed, extending anteri- 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 

LI ST 



29 




PG BG 



Fig. 34 Yoldiella sinuosa. Lateral view 
from the right side of the internal 
morphology of a specimen from Sta. 299 
Guyana Basin. (Scale = 1.0 mm). 



orly on either side of the stomach, anterior to the lateral 
pedal retractor muscles. It also pentrates the foot posterior to 
the stomach. 

Only male specimens were observed in which the testes 
were restricted to the anterior dorsal and ventral limits of the 
viscera. 

Yoldiella sinuosa is characterized by its slightly sinuous 
postero-ventral shell margin and the s-shaped course of the 
hind gut (see p. ). 

Yoldiella blanda (new species) 

Type locality. R.V. Atlantis II, Cruise 60, Sta. 247, 
Argentine Basin, 17.3.1971, 43°32.0'S, 48°58.1'W, 
Epibenthic Trawl, 5208-5223 m. 

Type specimen. Holotype: BM(HM) 1992020, Paratypes: in 
a collection held by J. A. Allen. 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



ARGENTINE BASIN 

Atlantis II 242 4382- 119 38°16.9'S 51°56.1'E ES 13.3.71 
60 4402 

245 2707 1 36°55.7'S 53°01.1'E ES 14.3.71 
247 5208- 106 43°33.0'S 48°58.1'E ES 17.3.71 

5523 
252 4435 42 38°29.8'S 52°09.1'E ES 22.3.71 
256 3906- 63 52°19.3'S 52°19.3'E ES 24.3.71 

3117 
259 3305- 20 37 < T3.3'S 52°45.0'E ES 26.3.71 

3317 



50r 



W/L 



H/L 



40 

70 
60 



60r- 
PL/TL 



40 L 



• • «• 



. . / 






Length(mm) 



n 
4 



j This species is restricted to abyssal depths in Argentine 
I Basin. Depth range: 2707-5223 m. 

Shell description (Figs. 36 & 37). Shell ovate, laterally 



Fig. 35 Yoldiella sinuosa. Variation in the ratios of height H/L, 
width W/L, and post-umbonal length PL/TL to length against 
length of a subsample from Sta. 299 Guyana Basin. 

compressed, fragile, slightly inequilaterial; umbos small, not 
markedly raised or inflated, slightly anterior to the mid line; 
antero-dorsal, anterior and ventral margins, evenly curved, 
postero-dorsal margin slopes in almost straight line from 
umbo, anterior and posterior limits dorsal to mid horizontal 
line; hinge plate moderately strong, parallel to dorsal margin, 
anterior and posterior series of teeth equal in number; 
ligament amphidetic and extends slightly below hinge plate 



30 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



with very small anterior and posterior marginal extensions of 
fused periostracum. 

Internal morphology (Fig. 38). Exhalent and inhalent 
siphons combined, the inhalent siphon is shorter than the 
exhalent and open at the ventral margin. There is a siphonal 
tentacle to the left side. The posterior adductor muscle is oval 
and approximately half the size of the crescent-shaped ante- 
rior muscle. The gills are moderately well-developed and the 
plates number up to 16. The labial palp ridges number 
between 14-18 depending on size of individual. The foot is 
large with a conspicuous byssal gland. There is a single hind 
gut loop to the right of the body which has a characteristic 
course that approaches an 'S' in shape. 

Prodissoconch length: 198 (xm. Maximum recorded shell 
length: 5.61 mm. 

Most closely resembles Y. sinuosa but without the postero- 
ventral sinuosity (Fig. 139). 




Fig. 36 Yoldiella blanda. Lateral view of a shell from the right side 
and detail of the hinge-plate of a right valve. Specimens from Sta. 
242 Argentine Basin. (Scale = 1.0 mm). 




Fig. 37 Yoldiella blanda. Outline drawings of shells of differing 
sizes from the right side to show change in shape with growth. 
Specimens from Sta. 242 Argentine Basin. (Scale = 1.0 mm). 




Fig. 38 Yoldiella blanda. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 242 Argentine 
Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34. 

Yoldiella biscayensis (new species) 

Type locality. R.V. Chain, Cruise 106, Sta. 326, Bay of 
Biscay, 22.8.1972, 50°04.9'N, 14°23.8'W, Epibenthic Trawl, 
3859 m. 

Type specimen. Holotype BM(NH) 1992024, Paratypes: in 
collection held by J.A. Allen. 

Material. 



Cruise 



Sta 



Depth No 
(m) 



Lat 



Long 



Gear Date 



WEST EUROPEAN BASIN 



Jean Charcot 












(Polygas) 


DS20 4226 


10 


47°33.0'N 


9°36.7'W 


DS 


24.10.72 




DS21 4190 


6 


47°31.5'N 


9°40.7'W 


DS 


24.10.72 




DS22 4144 


21 


47°34.1'N 


9°38.4'W 


DS 


25.10.72 




DS23 4734 


17 


46°32.8'N 


10°21.0'W 


DS 


26.10.72 


(Biogas II) 


DS31 2813 


11 


47°32.5'N 


9°04.2'W 


DS 


19. 4.73 


(Biogas III) 


DS44 3992 


4 


47°33.2'N 


9°42.0'W 


DS 


27. 8.73 




DS41 3548 


20 


47°28.3'N 


9°07.2'W 


DS 


26. 8.73 




DS45 4260 


6 


47°33.9'N 


9°38.4'W 


DS 


27. 8.73 




DS48 4203 


2v 


44°29.0'N 


4°54.0'W 


DS 


31. 8.73 


(Biogas IV) 


DS53 4425 


11 


44°30.4'N 


4°56.3'W 


DS 


19. 2.74 




DS54 4659 


20 


46°31.1'N 


10°29.2'W 


DS 


21. 2.74 




DS55 4125 


76 


47°34.9'N 


9°40.9'W 


DS 


22. 2.74 




DS56 4050 


1 


47°32.7'N 


9°28.2'W 


DS 


23. 2.74 




DS59 2790 


3 


47°31.7'N 


9°06.2"W 


DS 


24. 2.74 




DS60 3742 


24 


47°26.8'N 


9°07.2'W 


DS 


24. 2.74 




KR35 4140 


1 


47°26.0'N 


9°08.7'W 


KR 


25. 2.74 


(Biogas V) 


DS66 3480 


31 


47°28.2'N 


9°00.0'W 


DS 


16. 6.74 




DS67 4150 


4 


47°31.0'N 


9°35.0'W 


DS 


17. 6.74 




DS68 4550 


2+2v 46°26.7'N 


10°23.9'W 


DS 


19. 6.74 




DS69 4510 


1 


44°21.9'N 


4°52.4"W 


DS 


20. 6.74 




DS70 2150 


1 


44°08.8'N 


4°17.4'W 


DS 


21. 6.74 


(Biogas VI) 


DS74 2777 


7 


47°33.0'N 


9°07.8'W 


DS 


22.10.74 




DS75 3250 


9 


47-28.1'N 


9°07.8'W 


DS 


22.10.74 




DS76 4228 


101 


47°34.8'N 


9°33.3'W 


DS 


23.10.74 




DS77 4240 


11 


47°31.8'N 


9°34.6'W 


DS 


24.10.74 




DS78 4706 


47 


46°31.2'N 


10°23.8'W 


DS 


25.10.74 




DS79 4715 


106 


46°30.4'N 


10°27.1'W 


DS 


26.10.74 




DS80 4720 


19 


46°29.5'N 


10°29.5"W 


DS 


27.10.74 




DS81 4715 


9 


46°28.3'N 


10°24.6'W 


DS 


27.10.74 




DS82 4462 


27 


44°25.4'N 


4°52.8'W 


DS 


29.10.74 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



31 





DS85 4462 


2 


44°23.2'N 


4°50.8'W 


DS 


30.10.74 




CP13 3134 


2 


47°34.4'N 


9°38.0'W 


CP 


23.10.74 




CP16 4825 


1 


46°27.3'N 


10°25.0'W 


CP 


26.10.74 




CP17 4706 


2 


46°30.8'N 


10°19.5'W 


CP 


26.10.74 




CP19 4434 


1 


44°24.9'N 


4°51.3'W 


CP 


28.10.74 




CP22 4475 


2 


44°22.9'N 


4°54.8'W 


CP 


30.10.74 


Jean Charcot CPU 4823 


1 


48°20.4'N 


15°14.6'W 


CP 


1. 8.76 


(Incal) 


OS02 4829 


2 


48°19.2'N 


15°15.7'W 


OS 


2. 8.76 




WS03 4829 


3 


48°19.2'N 


15°23.3'W 

15°22.5'W 


ws 


1. 8.76 




DS14 4254- 


7 


47°32.8'N 


9°35.4"W 


DS 


7. 8.76 




4348 














DS15 4211 


6 


47°33.6'N 


9°39.1'W 
- 9°38.5'W 


DS 


8. 8.76 




DS16 4268 


13 


47°29.8'N 
- 47°30.3'N 


9°33.4'W 


DS 


9. 8.76 




OS05 4296- 


4 


47°31.3'N 


9°34.6'W 


DS 


7. 8.76 




4248 




- 47°32.2'N 


9°34.7'W 








OS06 4316 


5+l\ 


47°27.3'N 


9°36.2'W 


OS 


9. 7.76 


in*9.347°27.9'N 






9°36.0'W 






int3.9OS07 


4249 


12 


47°31.8'N 
- 47°31.3'N 


9°34.3'W 


OS 


10.8.76 




OS08 4327 


13 


47°29.8'N 
■ 47°29.5'N 


9°32.9'W 
9°38.8"W 


OS 


11. 8.76 




WS07 4281 


9 


47°30.6'N 
- 47°31.2'N 


9°37.1'W 
9°35.7'W 


WS 


7. 8.76 




WS08 4287- 


13 


47°30.5'N 


9°33.7'W 


WS 


9. 8.76 




4301 




■ 47°29.3'N 


9°34.1'W 








WS09 4277 


8 


47°28.8'N 
■ 47°27.9'N 


9°34.0'W 


WS 


10. 8.76 




WS10 4354 


18 


47°27.3'N 
■ 47°28.2'N 


9°39.9"W 

12°43.9'W 


WS 


11. 8.76 




KR07 2891 


8 


55°02.9'N 


12°43.9'W 


KR 


20. 7.76 


Chain 106 


321 2890- 
1868 


2 


50°12.3'N 


13°35.8'W 


ES 


20. 8.76 




323 3356- 


39 


50°08.3'N 


13°53.7'W 


ES 


21. 8.76 




3338 




- 


13°50.9'W 








326 3859 


29 


50°04.9'N 


14°23.8'W 


ES 


22. 8.76 




328 4426- 


13 


50°04.7'N 


15°44.8'W 


ES 


23. 8.76 




4435 














330 4632 


29 


50°43.5'N 
■ 50°43.3'N 


17°51.7'W 
17°52.9'W 


ES 


23. 8.76 



Restricted to abyssal depths in West European Basin, the 




Fig. 39 Yoldiella biscayensis. Lateral view of a shell from the right 
side and detail of the hinge-plate of a left valve. Specimens from 
Sta. 326 West European Basin. (Scale =1.0 mm). 



majority of specimens were taken from depths greater than 
3500 mm. Depth range: 2150-4829 m. 

Shell description (Figs. 39-42). The form of the shell 
varies somewhat from locality to locality. 

Form A: The following description is based on specimens 
found in Bay of Biscay at 4000 m and below. 




Fig. 40 Yoldiella biscayensis. Outline drawings of shells of 
different sizes from the right side to show change in shape with 
growth. Specimens from Sta. 326 West European Basin. (Scale 
1.0 mm). 





Fig. 41 Yoldiella biscayensis. Outline drawings of three shells of 
similar size from the right side to show differences in shape. 
Specimens a & b from Sta. BGVI DS 76 (4228 m); specimen c 
from Sta. BG II DS 31 (2813 m). (Scale = 1.0 mm). 



32 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



40 



30 



80 



W/L 



a. * *»°* • d *a d 



H/L 



9* 



*T:**Aa 4 /' 



.-•v 



60 J 

60 

50H 



PL/TL 






Length (mm) 

Shell compressed, ovate, fragile, inequilateral, post- 
umbonal length 48-62% of total length, sculpture of fine 
irregular concentric lines, pale yellow periostracum; umbo 
slightly raised, posteriorly directed; antero-dorsal margin 
convex curving gradually to broadly rounded anterior mar- 
gin, ventral margin evenly curved, postero-dorsal margin 
very slightly sinuous, slopes gradually to distal limit of hinge 
plate, then more sharply inclined to posterior margin; hinge 
plate moderately long, moderately well-developed with up to 
10 well developed teeth on each side of ligament, occasionally 
one additional tooth in posterior series; ligament amphidetic, 
large, internal, goblet-shaped, extends ventral to and some- 
what posterior to proximal limit of posterior hinge plate. 

Prodissoconch length: 187-198 u.m. Maximum recorded 
shell length: 5.82 mm. 

Form B: This was taken between approximately 
3000-4100 metres and at about 4000 m may be mixed with 
Form A. The shell is distinguished from Form A by a more 
marked concavity in the proximal part of the postero-dorsal 
margin and by a more rounded posterior margin. Internally 
the hinge and ligament are similar. Form B on average is 
somewhat smaller than Form A. 

Maximum recorded shell length: 4.19 mm. 

Form C: Recorded at 2076 and 1891 metre depths. This 
form is intermediate between Forms A and B. It has an 
almost straight postero-dorsal margin. 

Maximum recorded shell length: 7.39 mm. 

Internal morphology (Fig. 43). The three forms are 
anatomically indestinguishable from each other. Exhalent 
and inhalent siphons are combined. There is a siphonal 
tentacle that lies either to the left or the right of the siphons. 
A feeding aperture is present ventral to the siphon embay- 
ment and there is a well-developed anterior marginal sense 
organ. 

The adductor muscles have conspicuous 'quick' and 
'catch' parts. The posterior muscle is approximately half 
the size of the anterior and oval in outline. The anterior 
muscle is crescent-shaped. The gills are well-developed 
with a relatively large number (up to 28) of gill plates 
alternating on either side of the gill axis. The labial palps 



Fig. 42 Yoldiella biscayenesis . 
Variation in the ratios of height 
H/L, width W/L, and 
postero-umbonal length PL/TLL 
to length against length of the 
three shape forms illustrated in 
Fig. 41. Solid circles, angulate 
specimens from Sta. BG VI 
DS76; solid triangles, rounded 
specimens from Sta. BG VI 
DS76; open squares, specimens 
from Sta. BG II DS31; West 
European Basin. 



are relatively large and, depending on the size of the 
animal, have up to 25 internal ridges. The palp proboscides 
are long and thin. The foot is large with a large byssal 
gland. There is a small single papilla posterior to the 
aperture of the gland and the posterior surface of the foot 
is well-supplied with secretory cells. As in other species, 
there is histological evidence of a secretion being released 
along the whole length of the sole of the foot. Large, 
round, pedal ganglia are situated dorsal to the byssal gland. 
The visceral ganglia are 'club'-shaped and relatively slen- 
der, the cerebral ganglia are slightly more inflated. The 
oesophagus, stomach and style sac are similar to those 
described for other Yoldiella species, the hind gut is 
relatively broad and forms a single loop on the right side of 
the body. The posterior section of the loop describes a 
conspicuous and characteristic 'S'-shaped course. There is 
a typhlosole along the length of the hind gut. The digestive 
diverticula are similar to those of other species of Yoldiella. 
The sexes are separate. All individuals more than 3.0 mm 
in length show some gonadial development. A specimen 
4.9 mm in length contained 190 ova (maximum diam. 150 
fan). 

Most closely resembles Y. sinuosa and Y. blanda and 
distinguished by more angulate postero-dorsal margin and 
lack of postero-ventral sinuosity. 

Yoldiella lata (Jeffreys 1876) 

Type locality. Valorous Sta. 9, Davis Strait, 14.8.1875, 
59°10'N, 50°25'W, dredge, 1750 fms. 

Type species. Lectotype: U.S. Natl. Mus., No. 199695 as 
here designated. 

Specimens from Biogas Sta. DS87 are housed in the 
Museum National d'Histoire Naturelle, Paris. 

Leda lata Jeffreys 1876, p. 431 (in part). 

As is pointed out under Y. jeffreysi (p. 63) when the 
'Valorous' material was examined, it was found that two 
species had been grouped together under the name Leda lata. 
Furthermore, the original description is such that it is not 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



33 




Fig. 43 Yoldiella biscayensis. Lateral view from the right side of 
the internal morphology of a specimen from Sta. BG VI DS76 
West European Basin. (Scale = 1.0 mm). For identification of the 
parts see Fig. 34. 

possible to identify which of the two is L. lata. We have 
separated the two species and chosen lectotypes from the 
'Valorous' material. 



Material 














Cruise 


Sta DepthNo 


Lat 


Long 


Gear Date 




(m) 












WEST EUROPEAN BASIN 










Sarsia 


44 1739 


18 


43°40.8'N 


3°35.2'W 


ED 


16. 7.67 




65 1922 


25 


46°15.0'N 


4°50.0'W 


ED 


25. 7.67 


La Perle 














(Biogas I) 


DS06 
DS07 


3 
2 












DS11 2205 


8 


47°35.5'Ne 


8°33.7' 


WDS 8. 8.72 




DS12 2180 


2 


47°28.5'N 


8°35.5'W 


DS 


9. 8.72 




DS13 2165 


5+lv 


47°33.7'N 


8°39.9'W 


DS 


9. 8.72 




OS01 


2v 






OS 




Chain 106 


313 1491- 
1500 


457 


51°32.2'N 


12°35.9'W 


ES 


17. 8.72 




316 2173- 1653 


50°58.7'N 


13°01.6'W 


ES 


18. 8.72 




2209 












Jean Charcot 












(Polygas) 


DS15 2246 


8 


47°35.2'N 


8°40.1'W 


DS 


21.10.72 




DS16 2325 


1 


47°36.1'N 


8°40.5'W 


DS 


21.10.72 




DS18 2138 


10 


47°32.2'N 


8°44.9'W 


DS 


22.10.72 




DS25 2096 


255 


44°08.2'N 


4°15.7'W 


DS 


1.11.72 




DS26 2076 


1095 

+ 17v 


44°08.2'N 


4 o 15.0'W 


DS 


1.11.72 




CV10 2108 


2 


47°30.7'N 


8°40.6'W 


CV 


22.20.72 


Jean Charcot 












(Biogas II) 


DS32 2138 


26 


47°32.2'N 


8°05.3'W 


DS 


19. 4.73 


(Biogas III) 


DS35 2226 


9 


47°34.4'N 


8°40.7'W 


DS 


24. 8.73 




DS36 2147 


7+2v 


47°32.7'N 


8°36.5'W 


DS 


24. 8.73 




DS37 2110 


12+2v47°31.8'N 


8°34.6'W 


DS 


24. 8.73 




DS38 2138 


13 


47°31.5'N 


8°35.8'W 


DS 


25. 8.73 




DS49 1845 


177+ 
25v 


44°05.0'N 


4°15.6'W 


DS 


1. 9.73 




DS50 2124 


153+ 
61v 


44°09.9'N 


4°15.9'W 


DS 


1. 9.73 


(Biogas IV) 


DS51 2430 


421 + 
lOlv 


44°11.3'N 


4°15.4'W 


DS 


18. 2.74 




DS52 2006 


183 + 
190v 


44°06.3'N 


4°22.4'W 


DS 


18. 2.74 




DS61 2250 


3 


47°34.7'N 


8°38.8'W 


DS 


25. 2.74 





DS62 2175 


48+ lv 47°32.8'N 


8°40.0'W 


DS 


26. 2.74 


Jean Charcot DS64 2156 


12+ 


47°29.2'N 


8°30.7'W 


DS 


26. 2.74 






14v 












CV33 1913 


1 


44°04.6'N 


4°18.1'W 


CV 


18. 2.74 




CP01 2245 


19+4v 47°34.6'N 


8°38.8'W 


CP 


25. 2.74 


(Biogas V) 


DS70 2150 


6 


44°08.8'N 


4°17.4'W 


DS 


21. 6.74 




CP07 2170 


136+ 
4v 
19 


44°09.8'N 


4°16.4'W 


CP 


21. 6.74 


(Biogas VI) 


DS71 2194 


47°34.4'N 


8°33.8'W 


DS 


20.10.74 




DS86 1950 


325+ 
13v 


44°04.8'N 


4°13.7'W 


DS 


31.10.74 




DS87 1913 


550+ 

4v 

40+2\ 


44°05.2'N 


4°19.4'W 


DS 


1.11.74 




DS88 1894 


' 44°05.2'N 


4°15.7'W 


DS 


1.11.74 




CP08 2177 


12+ 1\ 


' 44°33.2'N 


8°38.5'W 


CP 


20.10.74 




CP09 2171 


34 


47°33.0'N 


8°44.1'W 


CP 


20.10.74 




CP24 1995 


23 


44°08.1'N 


4°16.2'W 


CP 


31.10.74 


Jean Charcot CP01 2068- 


29 


55°57.0'N 


10°55.0'W 


CP 


16. 7.76 




2040 












(Incal) 


CP02 2091 


4 


57°58.4'N 
• 57°57.7'N 


10°42.8'W 
10°44.6'W 


CP 


16. 7.76 




CP08 2644 


1 


50°14.7'N 


13°13.5'W 


CP 


27. 7.76 




- 




5015.2^ 


13°14.8'W 








OS01 2634 


2 


50°14.4'N 
50°15.2'N 


13°10.9'W 
13°11.0'W 


OS 


30. 7.76 




DS01 2091 


234 


57°59.7'N 
57°59.2'N 


10°39.8'W 
10°41.3'W 


DS 


15. 7.76 




DS02 2081 


262 


57°58.8'N 
57°58.5'N 


10°48.5'W 
10°49.2'W 


DS 


16. 7.76 




DS05 2053 


7 


56°28.1'N 
56°17.6'N 


H°11.7'W 
11°12.0'W 


DS 


18. 7.76 




DS06 2494 


86 


56°26.6'N 
56°15.9'N 


11°10.5'W 
11°10.7'W 


DS 


18. 7.76 




WS01 2550- 


6 


50°19.4'N 


13°08.0'W 


WS 


30. 7.76 




2539 




50°19.3'N 


13°06.9'W 








WS02 2498- 


4 


50°19.3'N 


12°55.8'W 


ws 


30. 7.76 




2505 




50°20.0'N 


12°56.0'W 







CANARIES BASIN 

Discovery 6701 1934 9 27°45.2'N 14°13.0'W ED 16. 3.68 

SIERRA LEONE BASIN 

Atlantis II 139 2099- 1 10°33.0'N 17°53.0'W ES 4. 2.67 
31 2187 

Largely restricted to lower slope and abyssal rise depths in 
the northeastern Atlantic, but predominantly in the West 
European Basin with a few specimens taken in the Canaries 
and Sierra Leone Basins. Depth range: 1491-3220 m. 

Shell description (Figs. 44 & 45). Shell transversely 
ovate, fragile, inequilateral, postumbonal length 53-65% 
of total length, moderately inflated, very fine concentric 
lines forming ridges ventrally, more conspicuous in larger 
specimens, irridescent, pale yellow/brown periostracum, 
light and dark banding patterns; umbo moderately inflated, 
inwardly directed; dorsal margin raised, anterior and pos- 
terior margins smoothly curved with anterior margin more 
convex than posterior, antero-dorsal margin short, joins 
anterior margin in smooth curve, postero-dorsal margin 
approximately straight, gradually inclining distally to pos- 
terior limit of hinge plate, then curves sharply to posterior 
margin, posterior margin more convex dorsally, ventral 
margin smoothly curved; hinge plate narrow, anterior and 
posterior hinge plates merge with margin below umbo, 
teeth small, chevron-shaped, number on each plate 
depending on size (up to 9/10), usually with one or two less 
on anterior hinge plate; ligament amphidetic, small, inter- 
nal rectangular in cross-section. 

Prodissoconch length: 198 |xm (average) range 190-220 
ixm. Maximum recorded shell length: 4.43 mm. 



34 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




6Ch 



Fig. 44 Yoldiella lata. Lateral view of a shell from the right side 
and detail of the hinge-plate of a right valve. Specimens from Sta. 
316 West European Basin. (Scale = 1.0 mm). 




Fig. 45 Yoldiella lata. Right lateral and dorsal views of shells to 
show changes in shape with growth. Specimens from Sta. 
INCAL/DS 06 West European Basin. (Scale = 1.0 mm). 

The shell is similar in shape to Yoldiella jeffreysi but more 
fragile, more compressed, and has fewer hinge teeth on a 
narrower hinge plate. With increasing length there is a 
gradual increase in the posterior umbonal length/total length 
ratio. There is little change in the height/length or width/ 
length ratios (Fig. 46). Hydroids are present on several 
specimens at the antero-ventral shell margin. 

Internal morphology (Fig. 47). With the exception of the 



-W/L 
40 

8CH 

H/L 
60- 
60n 



* * • ■ • . 

■ *!■ ■ a m L 






40 






PL/TL 



-JVJT 



^25 



15 No. 



3=L 



3 
Length 



Fig. 46 Yoldiella lata. Variation in the ratios of height H/L, width 
W/L and postero-umbonal length PL/TL to length against length 
of a sample from Sta. BG V CP 07 from the West European 
Basin. 




Fig. 47 Yoldiella lata. Lateral view from the right side of the 
internal morphology of a specimen from Sta. BG III DS 50 West 
European Basin (Scale = 1.0 mm). For identification of parts see 
Fig. 34. 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



35 



posterior margin, the mantle edge is little modified and 
comprises three marginal lobes. The middle sensory lobe 
forms a frill while the inner muscular fold is thickened, being 
approximately twice the thickness of the general mantle 
epithelium and is relatively broad. Posteriorly combined 
exhalent and inhalent siphons are formed by fusion of the 
opposing inner muscular lobes. The inhalent siphon is shorter 
than the exhalent siphon and remains open ventrally. The 
siphonal wall is relatively thin. A narrow band of longitudinal 
muscles lies immediately internal to the basal membrane of 
the outer and inner epithelia. Internal to the longitudinal 
fibres are circular and transverse muscle fibres with sub- 
epithelial gland cells scattered throughout the layer. Between 
the exhalent and inhalent siphons, there is a pair of haemo- 
coelic channels within the muscle layer (Fig. 48a). The 
proximal end of the gill axes join laterally at the junction 
between the siphons. The gill axes probably act as a channel 
to guide faecal rods into the lumen of the exhalent siphon. 
The anus lies immediately dorsal to the inner margins of the 
siphon. 

The siphonal tentacle, is developed from the middle sen- 
sory lobe of the mantle and originates from a pocket in the 
siphonal embayment at the base of the siphon, usually on the 
left side. It consists of an elongate finely-tapering cone which 
in transverse section comprises a large central nerve sur- 
rounded by several muscle fibres (Fig. 48b). These in turn are 
surrounded by a layer of connective tissue with gland cells 
interspersed throughout and a layer of epithelial cells with 
fine granular contents. 

Ventral to the siphon is a broad, deep, specialized area of 
the mantle - the feeding aperture. Ventral to the inhalent 
aperture there is an inner secondary muscular fold. Peripheral 
•to this the inner muscular layer is enlarged both in thickness 
and width. In preserved specimens this area is highly convo- 
luted. In life the muscular and sensory layers are probably 
extended beyond the shell margin as a flap on each side. The 
epithelial cells in this region are densely ciliated (Fig. 48a). 

The adductor muscles are unequal in size with the 'quick' 
and 'catch' parts obvious. The posterior adductor is round in 




outline. The anterior is approximately twice the size of the 
posterior and crescent-shaped. At the mantle margin ventral 
to the anterior adductor muscle there is a well-developed 
anterior sense organ. This is derived from the middle sensory 
fold which is greatly extended to form two flaps. The epithe- 
lial cells of the outer flap are ciliated. Internal to this the 
epithelium is glandular (Fig. 48c). Underlying this epithelium 
is a thick layer of connective tissue containing the pallial 
nerve. 

The gills lie parallel to the postero-dorsal shell margin. 
They are well-developed with up to 22 alternating gill plates 
(the number relates to the size of the individual). 

The labial palps are moderately large and, also depending 
on the size of the animal, have up to 24 ridges on their inner 
face. The palp proboscides are relatively slender. The palps 
are wedge-shaped and extend 1/4-1/2 way across the body. 
The mouth is set posterior to the anterior adductor muscle. 

The foot is well-developed, and of typical nuculanid form. 
The divided sole is elongate with papillate edges. At the tips 
of the papillae, lying between muscle fibres are glandular 
cells with ducts to the surface of the foot. Secretions from 
these may be used to lubricate the movement of the foot 
through the sediment. A large well-developed byssal gland is 
present in the heel of the foot (Fig. 49a). The byssal gland is 
spherical, composed of large, hyaline cells, surrounded by 
muscle fibres. It opens medially at the posterior limit of the 
divided sole and several glandular epithelial cells surround 
the opening. A very small medial papilla lies posterior to the 
opening at the heel of the foot. Histochemical tests have been 
carried out to identify type secretion from the gland. Tests 
did not confirm any protein component but this could have 
been masked by other muco-substances. The main compo- 
nent at the centre of the byssal gland appears to be a 
keratin-sulphate (PAS-ve with no glycol groups, and carboxyl 
groups). It has the character of cartilage. (Secretions from the 
gland cells in the foot do, however, possess carboyxyl 
groups). 

The posterior pedal retractor muscles comprise a thick, 
wide, strap that inserts on the shell on either side of the hind 
gut anterior to the posterior adductor muscle. A small 
postero-lateral pedal retractor muscle is present on either 
side of the stomach. Three major pairs of anterior pedal 
retractor muscles pass from the neck of the foot anteriorly to 
insert posterior to the anterior adductor muscle on either side 



PSA 





ig. 48 Yoldiella lata. Transverse sections through a, the inhalent, 
exhalent and feeding apertures; b, the base of the siphonal 
tentacle; c, the anterior sense organ of a specimen from Sta. BG 
III DS 49 West European Basin. (Scales = 0.1 mm). 



Fig. 49 Yoldiella lata, a, transverse section through the heel and 
'byssal' gland of the foot and b, right and left lateral external 
views of the stomach and style sac of specimens from Sta. Polygas 
DS 26 West European Basin. (Scales = 0.1 mm). 



36 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



of the oesophagus and lateral to the hind gut loop. 

The cerebral ganglia are relatively small and oval while the 
visceral ganglia are elongate and relatively thickened. The 
pedal ganglia are large and elongate/oval, conjoined, and 
each has a large dorsal statocyst associated with it and which 
contains numerous small refractile crystals. 

The mouth is displaced posteriorly to a small extent. It 
opens into a relatively long, ciliated oesophagus which curves 
first anteriorly to the posterior face of the anterior adductor 
before passing posteriorly to the stomach. The oesphagus is 
positioned almost centrally rather than dorsally within the 
body. The longitudinal axis of the stomach and style sac lies 
diagonally within the body, the style sac penetrating into the 
upper half of the foot. The stomach and style sac are large, 
taking up much of the central body space. Externally the 
stomach is brown in colour. A large gastric shield covers part 
of the dorsal wall and extends laterally, mainly to the left 
side. To the right of it are approximately nine sorting ridges. 
The organization of the stomach appears similar to that 
described for Ledella (Allen & Hannah, 1989). The stomach 
is cradled by the pedal retractor muscles. The digestive 
diverticla are in three parts which for the most part lie 
anterior to the stomach but also to the right and left of the 
body. A duct from the right diverticulum joins the stomach 
on the right anterior face just ventral to the oesophageal 
opening. Immediately posterior to this, a duct from one of 
the two left diverticula enters the stomach on the lower left 
side (Fig. 49b). The third diverticulum opens into the stom- 
ach immediately below the tooth of the gastric shield. The 
epithelial cells which line these ducts contain highly refractile 
golden granules. In the case of the third diverticulum the duct 
is reduced to a small collar of cells around the aperture. 
Material was present in the lumen of this diverticulum but not 
in the other two diverticula. 

From the style sac, the hind gut passes posteriorly into the 
foot, as far as the pedal ganglia. It then passes anterior for a 
short distance between ganglia and byssal gland and then 
takes a dorsal course parallel to the posterior margin of the 
foot to a point immediately ventral to the ligament. It then 
forms a loop on the right side of the body which skirts the 
posterior face of the anterior adductor and then passes 
dorsally and posteriorly parallel to shell margin to the anus. 
A deep typhlosole is present along the entire length of the 
hind gut. Slight variations in the arrangement of the loop of 
the hind gut are seen in this species. Material in the gut 
consists of fine clay particles and skeletal fragments of various 
kinds. 

The sexes are separate. The gonads overlie the lateral and 
dorsal sides of the viscera of the body. Gonads are present in 
all specimens over 2 mm in length. Numbers of ova are 
relatively high and vary with the size of the animal. A 
maximum of c.730 ova were counted in a specimen 3.54 mm 
in length. The maximum observed diameter of the ova range 
from 126-190 |xm. There is some indication of an annual 
reproductive cycle. Ova of maximum size were present in 
October and February. April and June samples show little 
ovarian development, but increasing maturity was observed 
in July and August. The gonadial apertures open into the 
supra-mantle cavity, close to those of the kidney, anterior to 
the posterior pedal retractor muscle. 

The kidney is well-developed. It lies anterior to the poste- 
rior pedal retractor muscle and extends on either side of the 
stomach, tapering to its anterior limit close to the lateral 
pedal retractor mucles. The kidney epithelium is a single 



layer of cuboid cells. The heart, through which the hind gut 
passes is well-developed in this species with numerous muscle 
fibres in a relatively thick-walled ventricle. 

Distinctive features include the hind gut on the right hand 
side of body forming an extended single loop which turns 
back on itself; the light and dark banding pattern of shell, and 
the more rounded posterior adductor muscle. The hind gut, 
although similar, is simpler in form than that in Yoldiella 
jeffreysi. 

Yoldiella frigida Torrell 1859 

Type locality. Spitzbergen, Ice Sound 55 m. 

Type specimen. Holotype not known; lectotype (desig. A. 
Waren, 1989) Swedish Museum of Natural History No. 1986. 

Yoldia frigida Torrell 1859, p. 148, pi. 1, Fig. 3; Friele 1878, p. 

222; Leche 1878, pi. 1, Fig. 6 a-d; Sars G.O. 1878, pi. 4, 

Fig. lla-b; Friele 1879, p. 266. 
Leda frigida Jeffreys 1870, p. 440; Jeffreys 1879, p. 570. 
Pordandia frigida Norman 1893, p. 344, p. 364; Posselt 1898, 

p. 34-35; Friele & Grieg 1901, p. 15; Hogg 1905, p. 112; 

Jensen 1905, p. 320; Grieg 1909, p. 534; Ohdner 1915, pi. 

1, Figs. 30-32; 
Pordandia frigida Grieg 1916, p. 8; Ockelmann 1958, pi. 1. 

Fig. 14. 
Pordandia (Yoldiella) frigida Soot-Ryen 1939, p. 9; Clarke 

1963, p. 100, pi. 2, Figs. 6-8. 
Yoldiella frigida Soot-Ryen 1958, p. 10; Waren, 1989; Figs. 

7E&F&10G&H. 

Material. 



Cruise Sta Depth No 


Lat 


Long 


Geai 


Date 


(m) 










NORTH AMERICAN BASIN 










Atlantis 4 400 304 


39°56.6'N 


70°39.9'W 


AD 


30. 8.62 


Chain 58 105 530 121 


39°56.6'N 


71°03.6'W 


ET 


5. 5.66 


Chain 88 207 805- 153 


39°51.3'N 


70°54.3'W 


ES 


21. 2.69 


811 


39°51.0'N 


70°56.4'W 






WEST EUROPEAN BASIN 










Thalassa 2425 700 1 


48°28.9'N 


09°44.0"W 


PBS 


25.10.73 


Jean Charcot DS04 619 1 


57°23.0'N 


11°07.0'W 


DS 


17. 6.76 


Incal DS03 609 16 


57°25.1'N 


11°03.7'W 


DS 


17. 6.76 



In addition to the above, material from Ingolf Sta. 115 (det 
Ockelmann), Spitzbergen, Franz Joseph Fjord, East Green- 
land (USNM No. 219726 det. Odhner) and off Martha's 
Vineyard Sta. 934 (USNM No. 193343 det. Verrill & Bush) 
has been examined. 

Predominantly a North Atlantic high arctic species from 
shelf seas and upper slope depths (Waren (1989). Clarke 
(1963) reports it as being present at abyssal rise depths but 
there must be some doubt about this. There is some indica- 
tion that in north temperate seas at the southern extremity of 
its range the population is found deeper at the shelf slope 
break, thus suggesting a relationship with temperature. 
Greenland, Jan Mayen, Spitzbergen, Novaya Zemlya, Kera 
Sea, West Siberia, Iceland, North American and West Euro- 
pean Basins (see Ockelmann (1958) for other more doubtful 
records). Depth range: 5-811 m. 

Shell description (Fig. 50 & 51). Shell subelliptical, 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



37 




Fig. 50 Yoldiellafrigida. Lateral 
views of shells from the right side. 
Specimens a & b from Franz Joseph 
Fjord, E. Greenland; c, from Sta. 
INCAL DS 04 Bay of Biscay; d, from 
off Martha's Vinyard (USNM No. 
193343). (Scale = 1.0 mm). 



approximately equilateral (postumbonal length 45-50% of 
total length), smooth, moderately thin, pale yellow irrides- 
cent periostracum, with banding patterns, narrow dark bands 
and broader light bands between; umbo slightly raised 
directed somewhat posteriorly; dorsal margins proximally 
straight, distally curving to anterior and posterior margins, 
posterior and anterior dorsal margins very slightly angulate at 
limit of hinge plate, limit of anterior margin submedial, limit 
of posterior margin supramedial, postero-ventral margin rela- 
tively flattened, very slightly sinuous particularly in larger 
specimens; hinge plate relatively short, not extending beyond 
inner margin of adductor muscles, 5 anterior teeth and 6 
posterior teeth in specimen 2.5 mm, ventral part of chevron 
reduced; ligament amphidetic, large elongate internal part, 
with small external extensions either side of umbo; adductor 
muscle scars distinct, particularly anterior, line of attachment 
of pallial sinus also visible. Hydroids may be present, dor- 
sally, close to umbo and on the posterior and postero-ventral 
margins. 
Prodissoconch length: 166-208 |xm. Maximum recorded 




Fig. 51 Yoldiella frigida. Lateral views of left valves showing detail 
of the ligament and the hinge-plates; a, a specimen from Stor 
Fjord Spitzbergen (USNM No. 219726); b, a specimen from Sta. 
105 North America Basin. (Scale = 1.0 mm). 



shell length: 3.98 mm, (Sta. 207), however, specimens from 
Greenland donated by Ockelmann measure 6.1 mm. 

Comparing height/length, width/length and post-umbonal 
length/total length ratios of specimens from the North Ameri- 
can Basin (Sta. 105 & 207) and West European Basin (Incal 
DS03), it was found that in the latter case the average for 
each of the three parameters is slightly less than those from 
the two North American Stations and whose ranges for the 
most part overlap (Figs. 52 & 53). Specimens from Sta. 105 
appear to be somewhat wider than specimens from Sta. 207. 

It is highly likely that many records of Y. frigida from the 
North Atlantic relate to other species. This is a view also 
expressed by Waren (1989). For example, Y. frigida (USNM 
No. 193343) figured by Verrill & Bush (1898) and here (Fig. 
50), closely resembles Yoldiella nana again confirming the 
observations of Waren (1989). (Y. nana has a straighter 
dorsal margin, a slightly more inflated umbo and fewer hinge 
teeth). Further comparing USNM No. 193343 with high arctic 
specimens of Y. frigida the former has a larger umbo, and 
thicker hinge. In addition, we believe that many shallow 
water specimens of Yoldiella inconspicua from the North 
American Basin have been misidentified as Y. frigida. Subtle 
differences seen here, as in many other deep-sea protobranch 
bivalves, are particularly difficult to disentangle (Fig. 53) and 
in the case of Yoldiella this particularly applies to species 
found at shallower slope depths. 

Internal morphology (Fig. 54). Mantle structures include 
a well-developed anterior sense organ and long slender 
combined siphons with a single lumen. A siphonal tentacle is 
present originating, but not without exception, on the left 
side of the inner limit of the siphon embayment. The adduc- 
tor muscles are unequal in size the anterior being the some- 
what larger and oval in outline whereas the posterior muscle 
is more circular in outline. The gill axes attach ventrally to the 
siphon and with the exception of the ventral margin, the 
latter must be assumed to be largely exhalent in origin. There 
is a well-developed feeding aperture ventral to the siphon. 
The gills are well-developed, the number of filaments range 
from 12-22 according to the size of the specimen. The palps 
are large and extend over approximately half the length of the 
body. There are between 11 and 20 relatively broad palp 
ridges and the palp proboscides are also well-developed. The 



38 
50 



W\L 



30 J 
80 



60 
60 



H\L - A 



AA A 



A . A 



• A A .A 

. .A A * 



40 



PL\TL 



2 3 

Length (mm) 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 



Fig. 52 Yoldiella frigida. Variation in ratios of 
height H/L, width W/L and postero-umbonal length 
PL/TL to length against length of samples from; 
open triangles, Sta. 105 North America Basin; 
closed triangles, Sta. INCAL DS 03 Bay of Biscay; 
closed circles Sta. 207 North America Basin. 




foot which tends to be largely hidden by palps is also 
relatively large with well-developed retractor muscles. This is 
particularly true of the anterior series. There is a moderate- 
sized byssal gland. The pedal ganglia are elongate each with a 
large statocyst dorsal to it. The visceral ganglia lie relatively 
ventral in position, distant from the posterior section of the 
hind gut. The visceral and the cerebral ganglia are not 
particularly large. 

The gut describes a single loop on the right side of the 
body. The size of the hind gut and the path it describes on the 
right side of the body is highly characteristic of a species even 
in those with a single loop and is particularly useful in 
distinguishing, for instance, Y. frigida from Y. inconspicua 
(Figs. 53 & 63). The oesophagus is particularly wide in 
cross-section, the stomach is large with two sorting areas 
clearly visible to the right side of the gastric tooth. The more 
ventral of the two, which has not been observed in other 



Fig. 53 Yoldiella frigida. Outlines of shells 
from the right side from three Stations to 
show variation in shape within and between 
populations and with increasing size. 
Specimens from a, Sta. Ingolf 115 (det 
Ockelmann); b, Sta. 105 North America 
Basin; c, Sta. INCAL DS 03 Bay of Biscay. 
(Scale = 1.0 mm). 

species, is broad and close to the aperture of the right 
digestive duct. Ingested material was seen in the dorsal part 
of the left digestive diverticulum. The duct to the right 
digestive diverticulum overlies the dorsal section of the hind 
gut. The kidney is well-developed and the pericardial cavity is 
large. 

The sexes are separate. The developing gonads surround 
the hindgut loop in the usual manner. In one sectioned 
specimen (2.3 mm total length) 59 ova were present with a 
maximum diameter of 120 |xm. The ova were present ventral 
and internal to the digestive diverticula, with fewer numbers 
overlying the viscera dorsally. 






r . ; : 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 

Yoldiella robusta (new species) 

Type locality. R.V. Atlantis II, Cruise 60, Sta. 280, 
Argentine Basin, 29.3.1971, 36°18.0'S, 53°23.9'W, 
Epibenthic Trawl, 256-293 m. 



39 

Type specimen. Holotype : BM(NH) 1992030, Paratypes: in 
collection held by J. A. Allen. 

Material. 



Cruise Sta Depth No Lat Long 

(m) 



Gear Date 




Fig. 54 Yoldiella frigida. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 105 North America 
Basin. Inset is a right-frontal external view of the stomach. (Scale 
= 1.0 mm). For identification of parts see Figs. 34 & 49. 




ig. 55 Yoldiella robusta. Lateral view of a shell from the right 
side and detail of hinge-plate of a left valve. Specimens from Sta. 
280 Argentine Basin. (Scale = 1.0 mm). 



ARGENTINE BASIN 
Atlantis II 280 256- 3495 36°18.0'S 
293 



53°23.9'W ES 29.3.71 



Restricted to one Station at the shelf/slope break of the 
Argentine Basin. Depth range: 256-293 m. 

Shell description (Figs. 55 & 56). Shell subovate, moder- 
ately inflated, irregular concentric growth lines and small 
ridges best developed posteriorly, periostracum pale yellow; 
umbos anterior to mid line, slightly raised and inwardly 




Fig. 56 Yoldiella robusta. Outlines of shells from the right side to 
show change in shape with growth. Specimens from Sta. 280 
Argentine Basin. (Scale = 1.0 mm). 




Fig. 57 Yoldiella robusta. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 280 Argentine 
Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34. 



40 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



directed; proximal antero-dorsal margin horizontal for very 
short distance before curving steeply to anterior margin, 
proximal postero-dorsal margin horizontal or slightly convex, 
distally slightly angled opposite posterior limit of hinge, 
postero-ventral margin slightly sinous giving a relatively 
narrow rounded medial tip to posterior margin, ventral 
margin smooth convex curve. Hinge plate short, moderately 
narrow with up to 9 small chevron-shaped teeth on each 
series, one additional tooth on posterior plate. Ligament 
large, amphidetic, bilobed in lateral view, with short, narrow, 
secondary external extensions anterior and posterior to 
umbo. 

Prodissoconch length: c. 200 |xm. Maximum recorded shell 
length: 4.0 mm. 

Shell measurements (mm) & ratios are as follows:- 

Length Height Width H/L W/L PL/TL Teeth(A/P) 



1.89 


1.31 


0.70 


0.70 


0.37 


0.51 


- 


2.58 


1.76 


0.98 


0.68 


0.38 


0.53 


- 


2.62 


1.80 


0.94 


0.69 


0.36 


0.56 


- 


2.81 


1.89 


1.09 


0.67 


0.39 


0.55 


- 


3.05 


2.05 


1.23 


0.67 


0.40 


0.54 




3.44 


2.21 


0.64 


- 


- 


0.57 


8/9 


3.55 


2.38 


1.44 


0.67 


0.40 


0.55 


- 


3.61 


2.46 


0.68 


- 


- 


0.53 


7/8 


3.81 


2.67 


1.52 


0.70 


0.40 


0.56 


- 


3.98 


2.62 


1.58 


0.66 


0.40 


0.59 


- 



Internal morphology (Fig. 57). The internal morphology 
is very similar to that described for Y. frigida. The siphons are 
combined and there is a siphonal tentacle to the left. The 
anterior sense organ is well-developed. The adductor muscles 
are relatively large, the posterior being more round and 
slightly smaller than the anterior muscle. The foot is also 
large with a moderately-sized byssal gland. The gills are well 
developed and suspended more ventral within the mantle 
cavity than other species. There are approximately 15 alter- 
nating gill filaments. The labial palps extend across about half 
the body and have 12-16 internal ridges and well-developed 
palp proboscides. The visceral and cerebral ganglia are 
relatively large. The viscera are also more ventral in position 
than in most other Yoldiella species. The pedal ganglia are 
large and elongate. The hind gut forms a single loop on the 
right side of the body. 

Yoldiella externa (new species) 

Type locality. R.V. Atlantis II, Cruise 60, Sta. 245, 
Argentine Basin, 14.3.1971, 36o55.7'S, 53o01.4'W, 
Epibenthic Trawl, 2707 m. 

Type specimen. Holotype: BM(NH) 1992036, Paratypes: in 
collection held by J.A. Allen. 



Material. 








Cruise Sta Depth No 
(m) 


Lat 


Long 


Gear Date 


argentine basin 

Atlantis II 245 2707 26 
60 


36°55.7'S 


53°01.4'W 


ES 14.3.71 




Fig. 58 Yoldiella extensa. Lateral view of a shell from the right side 
and detail of the hinge -plate of a right valve. Specimens from Sta. 
245 Argentine Basin. (Scale = 1.0 mm). 

Shell description (Figs. 58 & 59). Shell oblong-ovate, 
moderately robust, moderately inflated, nearly equilateral, 
very fine concentric lines, periostracum pale yellow; umbo 
inflated, raised slightly, directed posteriorly; dorsal margin 
slightly convex, antero-dorsal margin gradually slopes to 
broad rounded anterior margin, ventral margin long, curva- 
ture similar to that of dorsal margin, posterior margin slightly 
extended with faint suggestion of postero-ventral sinus; liga- 
ment amphidetic, moderate size, elongate, but slightly asym- 
metric in lateral view with posterior part slightly longer and 
wider than anterior, slight external extension on either side of 
umbo; hinge plate narrow, relatively short, with small eden- 




Only found at the one Station at abyssal depth in Argentine 
Basin. Depth range: 2707 m. 



Fig. 59 Yoldiella extensa. Outlines of shells from the right side to 
show change in shape with growth (see also Fig. 58). Specimens 
from Sta. 245 Argentine Basin. (Scale = 1.0 mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



41 



tulous space below umbo, anterior plate follows curvature of 
antero-dorsal margin, posterior plate with slight convex arch, 
equal number of teeth on each plate, teeth with prominent 
dorsal arm and reduced ventral arm. 

Prodissoconch length: c 170 u.m. Maximum recorded shell 
length: 4.62 mm. 

Shell measurements (mm) & ratios are as follows:- 



Length 


Height 


Width 


H/L 


W/L 


PL/TL 


2.56 
2.60 


1.81 
1.76 


1.26 
1.22 


0.70 
0.68 


0.49 
0.47 


0.51 
0.53 



Internal morphology (Fig. 60). The siphons are com- 
bined, with a single lumen present. A siphonal tentacle 
occurs on the right side of the siphonal embayment. The 
adductor muscles are unequal in size the anterior being one 
and a half to two times larger in cross-section than the 
posterior. Both are more or less oval in shape. The gills are 
well-developed with 13-16 plates. The labial palps are small 
in the contracted state, extending about 1/4 distance across 
body, and have 8-10 moderately narrow palp ridges. In 
contrast the palp proboscides are well-developed. The pedal 
ganglia are large and elongate, similarly the visceral and 
cerebral ganglia are also well-developed. They are club- 
shaped with the cerebral ganglia being slightly larger than the 
visceral. The foot is long and narrow, with a large byssal 
gland in the heel. The stomach is large and there is a single 
hind gut loop on the right side of the body. 

Yoldiella inconspicua inconspicua Verrill & Bush 1898 

Type locality. Off Martha's Vineyard, 318 fm. Original 
specimens were taken from North American Basin between 
Lat. 42°33'N, Long. 69°58.5'W and Lat. 35°12.10'N and 
74°57.15'W by the U.S. Fish Commission Steamers Fish 
Hawk and Albatross. 







Fig. 60 Yoldiella extensa. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 245 Argentine 
Basin. (Scale = 1.0 mm). For identification of the parts see Fig. 
34. 



Type specimen. Holotype: U.S. Natl. Mus. No. 48867. 

Yoldiella inconspicua Verrill & Bush 1898, p. 869, pi. 79, 

Figs. 5-3. 
Yoldiella nana Waren 1989 (in part), p. 227. 

Material. 



Cruise 



Sta 



Depth No Lat 
(m) 



Long 



Gear Date 



WEST EUROPEAN BASIN 



Sarsia 


S44 1739 


11 


43°40.8'N 


3°35.2'W 


ED 


16. 7.67 




S50 2379 


343 


43°46.7'N 


3°38.0'W 


ED 


18. 7.67 


Jean Charcot DS20 4226 


2 


47°33.0'N 


9°36.7"W 


DS 


24.10.72 


(Polygas) 


DS21 4190 


3 


47°31.5'N 


9°40.7'W 


DS 


24.10.72 




DS22 4144 


3 


47°34.1'N 


9°38.4'W 


DS 


25.10.72 




DS28 4413 


2 


44°23.8'N 


4°47.5'W 


DS 


2.11.72 


Chain 106 


316 2173- 
2209 


20 


50°58.7'N 


13°01.6'W 


ES 


18. 8.72 




318 2868- 


72 


50°04.9'N 


14°23.8'W 


ES 


20. 8.72 




2890 




50°05.3'N 


14°24.8'W 








323 3338- 


16 


50°08.3'N 


13°53.7'W 


ES 


21. 8.72 




3356 




50°08.3'N 


13°50.9'W 








326 3859 


3 


50°04.9'N 
50°05.3'N 


14°23.8'W 
14°24.8'W 


ES 


22. 8.72 




330 4632 


30 


50°43.5'N 
50°43.4'N 


17°51.7"W 
17°52.9'W 


ES 


24. 8.72 


Challenger 


10 2540 


1 


56°36.0'N 


11°04.0'W 


ES 


4. 7.73 


Jean Charcot DS41 3548 


5 


47°28.3'N 


9°07.2'W 


DS 


26. 8.73 


(Biogas III) 














(Biogas IV) 


DS55 4125 


58 


47°34.9'N 


9°40.9'W 


DS 


22. 2.74 


(Biogas V) 


DS66 3480 


3 


47°28.2'N 


9°00.0'W 


DS 


16. 6.74 




DS67 4150 


1 


47°31.0'N 


9°35.0'W 


DS 


17. 6.74 


(Biogas VI) 


DS71 2194 


1 


47°34.3'N 


8°33.8'W 


DS 


20.10.74 




DS75 3250 


1 


47°28.1'N 


9°07.9'W 


DS 


22.10.74 




DS76 4228 


26 


47°34.8'N 


9°33.3'W 


DS 


23.10.74 




CP13 4134 


4 


47°34.4'N 


9°38.0'W 


CP 


23.10.74 




DS77 4240 


1 


47°31.8'N 


9°34.6'W 


DS 


24.10.74 




DS82 4462 


1 


44°25.4'N 


4°52.8'W 


DS 


29.10.74 


(Incal) 


DS01 2091 


2 


57°39.8'N 
57°59.2'N 


10°39.8'W 
10°41.3'W 


DS 


15. 7.76 




DS02 2081 


4 


57°58.8'N 
57°58.5'N 


10°48.5'W 
10°49.2'W 


DS 


16. 7.76 




C003 2466 


12 


56°38.0'N 
56°37.3'N 


H°64.0'W 
11°07.8'W 


CP 


17. 7.76 




C004 2483- 


9 


56°33.2'N 


11°11.3'W 


CP 


17. 7.76 




1513 




56°32.5'N 


11°12.4'W 








DS05 2503 


270 


56°28.1'N 
56°27.6'N 


11°11.7'W 
11°02.0'W 


DS 


18. 7.76 




DS06 2494 


277 


56°26.6'N 
56°25.9'N 


11°10.5"W 
11°10.7"W 


DS 


18. 7.76 




DS07 2884 


280 


55°00.7'N 
55°01.0'N 


12°31.0'W 
12°21.0'W 


DS 


19. 7.76 




DS08 2891 


58 


55°02.0'N 
52°01.9'N 


12°34.6'W 
12°33.4'W 


DS 


19. 7.76 




CP05 2884 


149 


55°O0.4'N 
55°00.9'N 


12°29.4'W 
12°31.1'W 


CP 


19. 7.76 




CP06 2888- 


218 


55°02.3'N 


12°40.3'W 


CP 


19. 7.76 




2893 




55°02.6'N 


12°41.7'W 








KR06 2891 


1 


55°02.9'N 
55°02.2'N 


12°43.7"W 
12°39.0'W 


KR 


20. 7.76 




KR07 2891 


1 


55°02.9'N 
55°02.2'N 


12°43.9'W 
12°39.0'W 


KR 


20. 7.76 




CP07 2895 


488 


55°03.4'N 
55°04.4'N 


12°46.2'W 
12°46.7'W 


CP 


20. 7.76 




DS09 2897 


867 


55°07.7'N 
55°08.1'N 


12°52.6"W 
12°53.2'W 


DS 


20. 7.76 




CP08 2644 


135 


50°14.7'N 
50°15.2'N 


13 13.5'W 
13°14.8'W 


CP 


27. 7.76 




DS10 1719 


21 


50°12.7'N 
50°13.2'N 


13°16.6'W 
13°16.4'W 


DS 


27. 7.76 



42 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 





QS01 2634 


322 


50°14.4'N 


13°10.9'W 


OS 


30. 


7.76 










50<T5.2'N 


13°11.0'W 










WS01 2550 


221 


50°19.4'N 


13°08.1'W 


ws 


30. 


7.76 










50°19.3'N 


13°06.9'W 










WS02 24S 


287 


50°19.3'N 


12°55.8'W 


ws 


30. 


7.76 










50°20.0'N 


12°56.0'W 










CP10 4823 


2 


48°25.5'N 


15°10.7'W 


CP 


31. 


7.76 










48°26.3'N 


15°09.8'W 










WS03 4829 


1 


48°19.2'N 


15°23.3'W 


ws 


1. 


8.76 




(broken valve) 


48°19.1'N 


15°22.5'W 










WS07 4281 


5 


47°30.6'N 


9°37.1'W 


ws 


7. 


8.76 










47°31.2'N 


9°35.7'W 










DS14 4254- 


1 


47°32.6'N 


9°35.7'W 


DS 


7. 


8.76 






4307 




47°32.9'N 


9°35.1'W 










OS06 4316- 


2 


46°27.3'N 


9°36.2'W 


OS 


9. 


8.76 






4307 




47°27.9'N 


9°36.0'W 










DS16 4268 


7 


47°29.8'N 


9°33.4'W 


DS 


9. 


8.76 










47°30.3'N 












QS07 4249 


2 


47°36.8'N 


9°34.3'W 


OS 


10. 


8.76 










47°31.3'N 


9°34.3'W 










QS08 4327 


1 


47°29.8'N 


9°39.2'W 


QS 


11. 


8.76 










47°29.5'N 


9°38.8'W 








NORTH AMERICA BASIN 












Atlantis II 


62 


2496 


25 


39°26.0'N 


70°33.0'W 


ET 


21. 


8.64 


12 


64 


2886 


80 


38°46.0'N 


70°06.0'W 


ET 


21. 


8.64 




72 


2864 


120 


38°16.0'N 


71°47.0'W 


ET 


24. 


8.64 




73 


1330- 
1470 


1 


39°46.5'N 


70°43.3'W 


ET 


25. 


8.64 


Chain 50 


76 


2862 


53 


39°38.3'N 


67°57.8'W 


ET 


29. 


6.65 




78 


3828 


3 


38°00.8'N 


69°18.7'W 


ET 


30. 


6.65 




85 


3834 


32 


37°59.2'N 


69°26.2'W 


ET 


5. 


7.65 




87 


1102 


17 


39°48.7'N 


70°40.8'W 


ET 


6. 


7.65 


Atlantis II 


126 


3806 


14 


39°37.0'N 


66°47.0'W 


ET 


24. 


8.66 


24 








39°37.5'N 


66°44.0'W 








Chain 106 


334 


4400 


5 


40°42.6'N 
40°44.0'N 


46°13.8'W 
46°14.6'W 


ES 


30. 


8.72 




335 


3882- 
3919 


12 


40°25.3'N 


46°30.0'W 


ES 


31. 


8.72 


Knorr 35 


340 


3264- 


95 


38°14.4'N 


70°20.3'W 


ES 


24.22.73 






3356 




38°17.6'N 


70°22.8'W 









We have examined the Verrill & Bush material housed in 
the U.S. National Museum. With the exception of specimen 
No. 49390, which is more inflated and slightly more inequilat- 
eral than is typical of specimens of Y. inconspicua and which 
is probably Y. frigida, the Verrill & Bush collection is 
correctly described. 

Waren (1989) synonymizes Y. inconspicua with Y. nana. 
We disagree with this view. Y. nana is essentially a high 
latitude species from the shelf and upper slope while Y. 
inconspicua s.s. is restricted to temperate latitudes at lower 
slope to abyssal depths in the North American and West 
European Basins. 

Depth range: 1102^829 m, but most common between 
2400-3000 m. 

Shell description (Fig. 61). The shell is very well 
described by Verrill & Bush (1898). We would add that 
although the shell is small, compressed and an ovate wedge- 
shape, the width, height and thickness of shell for any given 
length is variable (Fig. 62). Some specimens have a slightly 
sinuous postero-ventral margin. In many specimens the gut 
and internal organs are visible through a transparent shell, in 
others light and dark banding patterns are present on thicker 
shells. Hydroids may be present over most of the shell 
margin. The large elongate, slightly 'saddle-shaped', internal 
ligament is characteristic. The hinge teeth are small, the total 
number ranges from 6 in an individual 2.42 mm in length to 
13 in an individual of 3.44 mm in length. There is normally an 




Fig. 61 Yoldiella inconspicua inconspicua. Lateral views of shells 
from the right side and detail of hinge from a right valve; a, 
variation in shape of three specimens from Sta. 76 North America 
Basin with b, a specimen from Sta. INCAL CP 06 West European 
Basin. (Scale = 1.0 mm). 

additional tooth in the anterior series (3/3-7/6). Although the 
shape varies between individuals there is an overall trend of a 
slight increase in posterior umbonal length and in width with 
increasing shell length. The height ratio remains more or less 
constant (Fig. 62). Analysis of shell length of two samples 
from the east and west Atlantic showed marked size differ- 
ences (Fig. 64) probably indicative of the differences in time 
of successful settlements. Individual peaks in the sample from 
the Bay of Biscay perhaps might indicate an annual breeding 
event and a lifespan of 5 or 6 years. 
Shell measurements (mm) & ratios are as follows:- 



Length 


Height 


Width 


H/L 


W/L 


PL/TL 


4.20 


2.87 


1.66 


0.68 


0.39 


0.53 


4.03 


2.78 


1.54 


0.69 


0.38 


0.51 


3.79 


2.71 


1.53 


0.71 


0.40 


0.50 


3.66 


2.45 


1.43 


0.66 


0.39 


0.53 


3.58 


2.50 


1.38 


0.70 


0.38 


0.50 


3.41 


2.75 


- 


0.72 




0.53 


1.49 


1.02 


0.54 


0.69 


0.36 


0.48 


0.99 


0.76 


- 


0.77 


- 


0.48 


0.93 


0.62 


- 


0.67 


- 


0.50 



Internal morphology (Fig. 63). The morphology of the 
mantle is essentially the same as in other nuculanoid species. 
There are typically three mantle lobes. Specialization of the 
mantle margin includes an anterior sense organ, in position 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



43 



50 



40-, 



W\L 



30 J 
80 



H1L 






60 
60 
50^ 



PLITL 



Length (mm) 

Fig. 62 Yoldiella inconspkua inconspicua . Variation in the ratios 
of height H/L, width W/L and postero-umbonal length PL/TL to 
length against length of a sample from Sta. INCAL CP 08 West 
European Basin. 

vertically below the anterior adductor muscle. A large sipho- 
nal tentacle is usually attached on the right side of the 
innermost wall of the siphonal embayment, but was recorded 
on the left in a few specimens. Siphons are combined and 
form a wide tube with a single lumen. The feeding aperture is 
not particularly well-developed, being represented in Y. 
inconspicua by two small flaps ventral to the combined 
siphon. The inner muscular layer is not expanded anterior to 
these, as it is in some other Yoldiella species. The adductor 
muscles are large and approximately equal in size. The 
posterior muscle is circular and the anterior more 'crescent- 
shaped'. 
The gills are well-developed and filaments number from 




Fig. 63 Yoldiella inconspicua inconspicua. Lateral view from the 
right side of the internal morphology of a specimen from Sta. 72, 
North Atlantic Basin. (Scale = 1.0 mm). For identification of the 
parts see Fig. 34. 




2 3 

Length (mm) 



Fig. 64 Yoldiella inconspicua inconspicua. Length frequency 
histograms of two samples from a, Sta. 72 North America Basin 
and b, Sta. INCAL CP 08 West European Basin. 



12-23, the latter in a large individual 3.55 mm in length. The 
distal gill filaments lie close to the siphon and the gill axis 
attaches to the siphon ventro-laterally. The labial palps are 
moderately large with between 12-22 ridges on the internal 
face. The palp proboscides are long and thin. The cerebral 
ganglia are large, the visceral ganglia are moderate in size and 
the pedal ganglia are large and elongate oval in shape. They 
lie more dorsal in position in the foot than in most other 
Yoldiella species. The foot is divided and fringed with papil- 
lae and has a large byssal gland in the heel. 

The oesophagus is distended and wide in diameter. The 
longitudinal plane of the stomach lies at an angle to the 
vertical sagittal plane, and anteriorly is displaced to the right 
while posteriorly it lies to the left. The stomach is large but 
somewhat laterally flattened. The style sac is small. The first 
section of the hind gut which lies within the foot is wide in 
section from thence it curves dorsally parallel to the posterior 
margin of the foot. At its dorsal limit of its course there are 
two small kinks to the left of the body (possibly a result of 
contraction in preserved specimens) before it crosses to the 
right side to form a single anterior loop the outline of which is 
characteristic of the species. The diameter of the gut appears 
to vary somewhat between populations, western Atlantic 
specimens appear to have a more slender hindgut although 
the dimensions fall within the overall range of eastern Atlan- 
tic specimens. A typhlosole is present along the whole length 
of the gut. A considerable amount of food material is 
frequently present in the left hand digestive diverticulum. 
The digestive diverticula extend well posterior within the 



44 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 65 Yoldiella inconspicua africana. 
Outlines a, of a shell from the right side 
and a left valve to show detail of the 
hinge-plate from Sta. 8532 6 Cape Verde 
Basin and b, two shells from the right 
side from Sta. 201 Angola Basin. (Scale 
= 1.0 mm). 



body. A large well-developed kidney extends anteriorly close 
to the posterior limit of the diverticula. 

The sexes are separate. The gonads lie dorsal and ventral 
to the viscera and anteriorly they occur internal to the 
digestive diverticula. A female 2.8 mm in length collected in 
July (Incal CP 07) contained 255 closely packed ova with a 
maximum diameter of 132 u.m. 

Yoldiella inconspicua africana (new subspecies) 

Type locality. R.V. Atlantis II, Cruise 42, Sta. 201, 
Angola Basin, 23.5.1968, 9°25'S, 11°35'E to 9°29'S, 11°34'E, 
Epibenthic Trawl, 1964 m. 

Type specimen. Holotype BM(NH) 1992039, Paratypes: in 
collection held by J.A. Allen. 

Material. 



Cruise 


Sta Depth 


No 


Lat 


Long 


Gear Date 




(m) 












SIERRA LEONE BASIN 












Atlantis II 


145 2185 


29 


10°36.0'N 


17°49.0'W 


ES 


6.2.67 


31 


147 3984 


5 


10°38.0'N 


17°52.0'W 


ES 


6.2.67 


CAPE BASIN 












Atlantis II 


192 2117- 


55 


23°02.5'S 


12°19.0'E 


ET 


17.5.68 


42 


2154 














194 2864 


28 


22°54.0'S 


11°55.0'E 


ET 


17.5.68 


ANGOLA BASIN 














201 1964 


109 


9°25.0'S 
■ 9°29.0'S 


11°35.0'E 
11°34.0'E 


ET 


23.5.68 


CAPE VERDE BASIN 












Discovery 


8521 ' 3058- 


2 


20°46.9'N 


18°53.4'W 


WS 


25.6.74 




3053 




■ 20°47.6'N 


18°53.5'W 








8521 6 3070- 


1 


20°47.9'N 


18°53.4'W 


WS 


26.6.74 




3964 




■ 20°48.6'N 


18°53.4'W 








8521 1 3113- 


34 


13°47.8'N 


18°14.0'W 


WS 


4.7.74 




3119 




■ 13°48.0'N 


18°14.8'W 








8532 6 2958- 


12 


13°48.2'N 


18°08.0'W 


WS 


5.7.74 




2952 




■ 13°47.6'N 


18°07.5'W 






Walda 


DS20 2514 


5 


2°32.0'S 


8°18.1'W 


DS 





Y. inconspicua africana is found off the West coast of Africa 
in the Sierra Leone, Cape Verde, Angola and Cape Basins at 
lower slope to abyssal depths. Depth range: 1964-3119 m. 

Shell description (Fig. 65). Shell very small, short, rela- 
tively compressed, ovate wedge-shape, very slightly inequi- 
lateral, except for some very fine lines shell surface smooth, 
periostracum pale yellow, iridescent; umbos just anterior to 
midline, slightly raised; antero-dorsal margin slightly convex, 
nearly horizontal close to umbos, then curving to slightly 
pointed anterior margin, ventral margin broadly rounded, 
often slightly swollen posteriorly, ascending steeply to poste- 
rior supramedial angle, postero-dorsal margin nearly hori- 
zontal close to umbo, then slightly convex, sloping gradually 
to posterior margin; posterior hinge plate narrow; teeth 
small, oblique v-shape, 4-5 on each hinge plate; ligament 
short, amphidetic, relatively wide, yoke-shaped, slight exter- 
nal extension on either side of umbo. 

Prodissoconch length: 166 |xm. Maximum recorded shell 
length 2.56 mm (Discovery Sta. 8521 b ). 

Internal morphology (Fig. 66). The siphons are com- 
bined but with a single lumen. The combined siphon is large 
and long, with relatively thin muscular walls. The single 
tentacle is large, attached to the right or the left at the base of 
the siphonal embayment. The feeding aperture is moderately 
well-developed with a small internal secondary fold. The 
mantle epithelial in the area of the feeding aperture and 
anterior to it is well supplied with gland cells, similar to those 
present in Yoldiella curta (p. 47). The anterior sense organ 
lies far anterior and is covered dorsally by an extended and 
particularly well-developed hood derived from the middle 
sensory lobe. The adductor muscles are slightly unequal in 
size; the larger anterior muscle is bean-shaped and the 
posterior is round in outline. The gills are well-developed 
with up to 12 filaments. The labial palps are relatively large 
with up to 15 broad ridges on the inner face. The palps extend 
across approximately one third of the body. The palp probos- 
cides are long and relatively slender. The foot is well- 
developed with a deeply divided sole. The byssal gland is 
moderately small. The ganglia are large. Both cerebral and 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



45 




Fig. 66 Yoldiella inconspicua africana. Lateral view from the right 
side of the internal morphology of a specimen from Sta. 8532 6 
Cape Verde Basin. (Scale = 1.0 mm). For identification of parts 
see Fig. 12. 

visceral ganglia are 'club'-shaped, the visceral being the 
larger. The ovoid pedal ganglia lie central in the foot, just 
dorsal and anterior to the byssal gland. A large statocyst lies 
dorsal to each pedal ganglion. 

The mouth is set posterior to the anterior adductor muscle. 
The oesophagus is relatively narrow while the stomach is 
large with a small style sac which does not penetrate the foot. 
The duct of the right digestive diverticulum passes dorsally 
around the hind gut to join the stomach close to the oesoph- 
ageal aperture. One of the two left diverticula opens ventral 
to the gastric tooth while the second opens adjacent to that 
from the right. No ingested material was observed in the 
diverticula. From the style sac, the hind gut passes between 
the pedal ganglia and the byssal gland before turning dor- 
sally. It makes a very small flexure on the left side immedi- 
ately before crossing to the right side at the dorsal limit of the 
body posterior to the ligament. On the right side of the body 
the hind gut makes a broad sweeping loop as far as the 
posterior face of the anterior adductor before passing dorsally 
and posteriorly to the anus. 

The gonads overlie the posterior, dorsal and dorso-lateral 
sides of the viscera and extend antero-dorsally with part lying 
centrally between the digestive diverticula. The kidney is 
small in comparison to the other species of Yoldiella 
described here, extending no further than the posterior edge 
of stomach. The heart is relatively large. 

This subspecies differs from Y. inconspicua s.s. in having a 
more elongate outline and a more pointed posterior shell 
margin. The dorsal margin is slightly more convex, the 
height/length ratio is slightly greater. The hind gut differs 
slightly in the course taken to the right of the body (Figs. 60 & 
66). 



Fig. 67 Yoldiella inconspicua projundorum. Lateral view of shell 
from the right side and detail of the hinge-plate of a left valve. 
Specimens from Sta. 242 Argentine Basin. (Scale = 1.0 mm). 

Yoldiella inconspicua profundorum (new subspecies) 

Type locality. R.V. Atlantis II, Cruise 60, Sta. 256, 
Argentine Basin, 24.3.1971, 37°40.9'S, 51°19.3'W, 
Epibenthic Trawl, 3906-3917 m. 

Type specimen. Holotype: BM(NH) 1992038, Paratypes: in 
collection held by J. A. Allen. 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



ARGENTINE BASIN 

Atlantis II 242 4382- 50 38°16.9'S 51°56.1'W ES 13.3.71 
60 4402 

243 3815- 1 37°36.8'S 52°23.6'W ES 14.3.71 

3822 
245 2707 2 36°55.7'S 53°01.4'W ES 14.3.71 
247 5208- 1 43°33.0'S 48°58.1'W ES 17.3.71 

5223 
252 4435 23 38°29.8'S 52°09.1'W ES 22.3.71 
256 3906- 19 37°40.9'S 51°19.3'W ES 24.3.71 

3917 
259 3305- 5 37°13.3'S 52°45.0'W ES 26.3.71 

3317 
264 2041- 6 36°12.7'S 52°42.7'W ES 28.3.71 

2048 

Restricted to the Argentine Basin at lower slope and abyssal 
depths. Depth range: 2041-5223 m. 

Shell description (Fig. 67). Shell small, equilateral, mod- 
erately inflated, subovate, fine concentric lines; umbos 
slightly raised, inwardly directed; shell outline somewhat 
variable, anterior and posterior dorsal margins straight proxi- 
mal to umbo, curve distally to broadly rounded anterior and 
slightly pointed posterior margins, ventral margin smooth 
curve; anterior and posterior hinge plates relatively narrow 



46 




Fig. 68 Yoldiella inconspicua profundorum. Lateral view from the 
right side of the internal morphology of a specimen from Sta. 242 
Argentine Basin. (Scale = 1.0 mm). For identification of the parts 
see Fig. 34. 



(but broader than in Y. inconspicuous s.s.) short, with up to 7 
teeth on each side; ligament amphidetic, large, slightly elon- 
gate, short external secondary extensions of fused perios- 
tracum on either side of umbo. 

The shell shape of this subspecies while similar to that of Y. 
inconspicua s.s. is slightly more rounded, in particular the 
posterior limit of the shell margin is medial instead of 
supramedial. The hinge plate is broader and the teeth stron- 
ger in Y. i. profundorum. 

Maximum recorded shell length: 3.31 mm. 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 
Shell measurements (mm) & ratios are as follows:- 



Length 


Height 


Width 


H/L 


W/L 


PL/TL 


2.90 
3.31 


2.09 
2.25 


1.25 
1.47 


0.72 
0.68 


0.43 
0.44 


0.52 
0.52 



Internal morphology (Fig. 68). Very similar to that of Y. 
inconspicua s.s. and Y. argentinea. In Y. i. profundorum, size 
for size, the posterior adductor muscle is more elongate than 
in Y. inconspicua s.s., the palps are slightly smaller and the 
ridges are broader but not as long and slightly fewer in 
number (12-14 internal ridges). 

Yoldiella argentinensis (new species) 

Type locality. R.V. Atlantis II, Cruise 60, Sta. 237, 
Argentine Basin, 11.3.1971, 36°32.6'S, 53°23.0'W, 
Epibenthic Trawl, 993-1011 m. 

Type specimen, presently housed in the Sanders collection. 
Woods Hole Oceanographic Institution, Paratypes: in collec- 
tion held by J.A. Allen. 

Material. 



Cruise Sta Depth No Lat Long 

(m) 



Gear Date 



53°31.6'W ES 11.3.71 
53°23.0'W ES 11.3.71 



ARGENTINE BASIN 
Atlantis II 236 497-518 3 36°27.0'S 
60 237 993- 26 36°32.6'S 

1011 
239 1661- 26 36°49.0'S 53°15.4"W ES 11.3.71 
1679 



Y. argentinensis has only been recorded from Argentine 




Fig. 69 Yoldiella argentinensis. 
Lateral view of the shells from the 
right side to show variation in shape; 
detail of the hinge-plate of a left 
valve; dorsal view of a shell. 
Specimens from Sta. 237 Argentine 
Basin. (Scales = 1.0 mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



47 



Basin at shelf slope break and upper slope depths. Depth 
range: 497-1679 m. 

Shell description (Fig. 69). Shell small, subovate, 
approximately equilateral, relatively compressed, 'boat- 
shaped' in outline except for fine concentric lines, smooth, 
iridescent; umbos inflated, inwardly directed; anterior and 
posterior dorsal margins concave proximal to umbo, distal to 
umbo slightly convex, slope gradually to anterior and poste- 
rior margins, anterior margin slightly produced, ventral mar- 
gin broadly curved, more convex posteriorly to slightly 
produced, posterior margin; horizontal axis supramedial; 
hinge plate short, teeth small, 'V-shaped, proximal teeth 
very small, difficult to discern, 6 anterior and 6 posterior in 
individual 3.66 mm long; ligament amphidetic, large with 
long, narrow, secondary external anterior and posterior 
extensions. 

Prodissoconch length: 150 |xm. Maximum recorded shell 
length: 4.03 mm. 

The shape of the shell is similar to that of Yoldiella 
inconspicua s.s. The main differences include the marked 
proximal concavities of the dorsal margin, the more inflated 
umbos and detail of the hinge. 

Internal morphology (Fig. 70). There is a wide combined 
siphon with a single lumen. The siphonal tentactle lies to the 
left side of the siphonal embayment. A feeding aperture is 
present ventral to the combined siphon. The adductor 
muscles are slightly unequal in size, in cross-section the 
posterior is broadly oval in outline while the larger anterior 
muscle is 'bean'-shaped. 

The foot is well-developed and there is a large byssal gland 
> in the heel. The gills are well-developed with between 10-17 
. alternating filaments (the number varying with the size of the 
individual). The labial palps are of moderate size, extending 
approximately one third across the body with between 10-18 
internal ridges. The hind gut forms a single loop on the right 
side of the body (Fig. 70). 

Yoldiella curta Verrill & Bush 1898 

JType locality. North America Basin, 40°16.5'N, 
67°05.3'W. 1290 fm. Original specimens were taken from the 
North America Basin between 41°11.5'N, 66°12.3'W and 




39°38'N - 70°22'W by U.S. Fish Commission Steamer Alba- 
tross, 5.10.1883, Beam Trawl. 

Type specimen. Holotype U.S. Natl. Mus. No. 38457. 

Phaseolus ovatus Verrill 1884, p. 230. 

Yoldia jeffreysi Verrill 1884, p.229; Verrill 1885, p. 576. 

Yoldia curta Verrill & Bush 1898, p. 868, pi. 97, Fig. 8; 

Waren 1989, p. 244. 
Yoldiella miniscula Verrill & Bush 1898, p. 870, pi. 79, Figs. 

2, 7; Waren 1989, p. 244, Figs. 14 A & B. 

Although a very well-defined species in that it is the only 
known Yoldiella with the hind gut configuration described 
below (p. 51), in its shell shape it is very similar to a number 
of other species. We believe that Y. miniscula Verrill & Bush 
is synonymous with it, indeed Verrill & Bush (1898) state this 
latter very minute species may, with a larger series, prove to 
be the young of one of the preceding species they describe. 
These latter include Y. inconspicua, Y. pachia, Y. lucida, Y. 
iris, Y. inflata, Y. subangulata, Y. lenticula and Y. curta. 
Verrill & Bush (1898) were correct in their supposition and 
here we illustrate specimens of Y. miniscula to show their 
similarity (Fig. 71). 

Note. The holotype specimen of Y. miniscula (U.S. Natl. Mus. 
No. 38415) is from the same Station as the holotype of Y. curta. 

Material. 



Fig. 70 Yoldiella argentinensis . Lateral view from the right side of 
the internal morphology of a specimen from Sta. 237 Argentine 
Basin. (Scale = 1.0 mm). For identification of the parts see Fig. 
34. 



Cruise 


Sta DepthNo 
(m) 


Lat 


Long 


Gear Date 


WEST EUROPEAN BASIN 










La Perle 


DS06 


1 










(Biogas I) 


DS07 


4 












DS12 2180 


1 


47°28.5'N 


8°35.5'W 


DS 


9. 8.72 




DS13 2165 


15 


47°33.7'N 


8°39.9'W 


DS 


9. 8.72 


Jean Charcot 












(Polygas) 


DS25 2096 


16+6v 44°08.2'N 


4°15.7'W 


DS 


1.11.72 




DS26 2076 


2 


44°08.2'N 


4°15.0'W 


DS 


1.11.72 




CV10 2108 


2v 


47°30.7'N 


8°40.6'W 


CV 


22.10.72 


(Biogas II) 


DS32 2138 


4 


47°32.2'N 


8°05.3'W 


DS 


19.4.73 


(BiogasIII) 


DS36 2147 


5 


47°32.7'N 


8°36.5'W 


DS 


24. 8.73 






(1 empty 4 dried) 










DS38 2138 


7+2v 


47°32.5'N 


8°35.8'W 


DS 


25. 8.73 




DS49 1845 


4+4v 


44°05.9'N 


4°25.6'W 


DS 


1. 9.73 


(Biogas IV) 


DS52 2006 


2+4v 


44°06.3'N 


4°22.4'W 


DS 


18. 2.74 




DS61 2250 


1 


47°34.7'N 


8°38.8'W 


DS 


25. 2.74 




DS62 2175 


10 


47°32.8'N 


8°40.0'W 


DS 


26. 2.74 




DS63 2126 


19+2v 47°32.8'N 


8°35.0"W 


DS 


26. 2.74 




DS64 2156 


7+4v 


47°29.2'N 


8°30.7'W 


DS 


26. 2.74 


(Biogas V) 


CP07 2170 


3 


44°09.8'N 


4°16.4'W 


CP 


21. 6.74 


(Biogas VI) 


DS71 2194 


7 


47°34.3'N 


8°33.8'W 


DS 


20.10.74 




DS86 1950 


28 


44°04.8'N 


4°18.7'W 


DS 


31.10.74 




DS87 1913 


7 


44°05.2'N 


4°19.4'W 


DS 


1.11.74 






(13+8v) 










DS88 1894 


5 


44°05.2'N 


4°15.4'W 


DS 


1.11.74 


Jean Charcot CP08 2177 


3 


44°33.2'N 


8°38.5'W 


CP 


20.10.74 


(Biogas VI) 


CP09 2171 


1 


47°33.0'N 


8°44.1'W 


CP 


20.10.74 


Jean Charcot CP01 2068- 


38 


57°57.7'N 


10°55.0"W 


CP 


16. 7.76 


(Incal) 


2040 




• 57°56.0'N 


10°55.0'W 








CP02 2091 


4 


57°58.4'N 
57°57.7'N 


10°42.8'W 
10°44.6'W 


CP 


16. 7.76 




DS01 2091 


468 


57°59.7'N 
57°59.2'N 


10°39.8'W 
10°41.3"W 


DS 


15. 7.76. 




DS02 2081 


544 


57°58.5'N 
57°58.5'N 


10°48.5'W 
10°49.2'W 


DS 


16. 7.76 




DS05 2503 


2 


56°28.1'N 
56°27.6'N 


11°11.7'W 
11°12.0'W 


DS 


18. 7.76 




DS06 2494 


6 


56°26.6'N 
56°25.9'N 


11°10.5'W 
11°10.7'W 


DS 


18. 7.76 



48 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 





OS01 2634 5 


Sarsia 


S-65 


1922 19 




33/2 


1537- 8 
1830 




S-44 


1739 68 


Chain 106 


313 


1500- 106 
1491 




316 


2173- 91 
2209 


NORTH AMERICA BASIN 


Atlantis II 


73 


1470- 699 


12 




1330 


Chain 50 


87 


1102 354 


Chain 58 


103 


2202 303 


Atlantis II 


115 


2031- 249 


24 




2051 


Atlantis II 


128 


1254 8 


30 


131 


2178 53 


Chain 88 


207 


805- 239 
811 




210 


2024- 4 
1064 


ARGENTINE BASIN 


Atlantis II 


239 


1661- 36 


60 




1679 




240 


2195- 1 



240 


2195- 
2323 


1 


264 


2041- 
2048 


4 


GUYANA BASirv 


[ 




Knorr 25 293 


2456- 
1518 


49 


295 


1000- 
1022 


25 


SIERRA LEONE BASIN 




Atlantis II 142 


1124- 


45 


31 


1796 




145 


2185 


1 


BRAZIL BASIN 






159 


834- 
939 


1 


167 


943- 
1007 


4 


169 


587 


6 


CAPE BASIN 






Atlantis II 189 


11007-496 


42 


1014 




190 


974- 
979 


7 


191 


1546- 
1559 


2 


Walda DS10 1432 


1 



50°14.4'N 13°10.9'W OS 30. 7.76 

50°15.2'N 13°11.0'W 

46°15.0'N 4°50.0'W ED 25. 7.67 

43°41.0'N 3°36.0'W AD 13. 7.67 

43°40'8'N 3°35'2'W ED 16. 7.67 

51°32.2'N 12°35.9'W ES 17. 8.72 

50°58.7'N 13°01.6'W ES 18. 8.72 

50°57.7'N 13°01.3'W 

39°46.5'N 70°43.3'W ET 25. 8.64 

39°48.7'N 70°40.8'W ET 6. 7.65 

39°43.6'N 70°37.4'W ET 4. 5.66 

39°39.2'N 70°24.5'W ET 16. 8.66 

39°46.5'N 70°45.2'W ES 15.12.66 

39°38.5'N 70°36.5'W ES 18.12.66 

39°39.0'N 70°37.1'W 

39°51.3'N 70°54.3'W ES 21. 2.69 

39°51.0'N 70°56.4'W 

39°43.0'N 70°46.0'W ES 22/23.2.69 

39°43.2'N 70°49.5'W 

36°49.0'S 53°15.4'W ES 11. 3.71 

36°43.4'S 53°10.2'W ES 23. 3.71 

36°12.7'S 52°42.7'W ES 28. 3.71 



8°58.0'N 54°04.3'W ES 27. 2.72 

8°04.2'N 54°21.3'W ES 28. 2.72 

10°30.0'N 17°51.5'W ES 5. 2.67 

10°36.0'N 17°49.0'W ES 6. 2.67 

7°58.0'S 34°22.0'W ES 18. 2.67 

7°58.0'S 34°17.0'W ES 20. 2.67 

- 7°50.0'S 

8°03.0'S 34°23.0'W ES 21. 2.67 

- 8°02.0'S 34°25.0'W 

23°00.0'S 12°45.0'E ES 16. 5.68 

23°05.0'S 12°45.0'E AD 17. 5.68 

23°05.0'S 12°31.5'E ES 17. 5.68 

18°40.0'S 10°56.3'E DS 



Y. curta is probably the most widely distributed species of 
Yoldiella. It occurs throughout the Atlantic at slope and 
abyssal rise depths. Depth ranges: 

Brazil Basin 587-1007 m 

Cape Basin 974-1559 m 

Guyana Basin 1000-1518 m 

Argentine Basin 1661-2048 m 

Sierra Leone Basin 1624-2185 m 

North American Basin 805-2178 m 

West European Basin 1537-2634 m 



Shell description (Figs. 71 & 72). Verrill & Bush (1898) 
give a full and accurate description of this species. Y. curta 
has a small, smooth, ovate, semi-transparent shell through 
which the characteristic, indeed unique, course of the hind 
gut is usually visible. The latter is usually seen as a double 
strand on the right side of the body with a single loop on the 
left extending out from the posterior margin of the anterior 
adductor. The hinge is short with a large internal ligament. 
The outline of the shell is variable both within (Fig. 73) and 
between populations. There is no lunule or escutcheon. The 
hinge plate is very short and slender and does not reach to the 
level of the inner margin of the adductor muscles. The 
number of teeth on each hinge plate varies with size up to a 
maximum of 7. There is usually one more tooth on the 
posterior hinge plate. The shell may be confused with other 
species e.g. Y. inconspicua, Y. lucida and Y. frigida, even 
though the hinge and the hind gut configuration are charac- 
teristic. 

In general, with increasing length, the height/length ratio 
increases thus producing a more rounded outline (Figs. 74 & 
75). The outlines of the anterior and posterior margins are 
variable. The anterior margin may be smoothly rounded or 
slightly angular, while the posterior margin is slightly 
extended with the degree of curvature and the position of the 
posterior limit in relation to the mid horizontal shell axis 
somewhat variable. With increasing size shells become more 
inequilateral with the posterior end slightly elongate. There is 
also a gradual increase in the width to length ratio. 

Prodissoconch length: 170 u.m. Maximum recorded shell 
length: 4.77 mm. 



Internal morphology (Figs. 76 a & b). As in other 
Yoldiella species the mantle is little modified and for the most 
part unfused. The inner muscular lobe is relatively broad and 
somewhat folded in preserved specimens. Posteriorly the 
inner muscular layer fuses to form a relatively wide, thin- 
walled combined siphon with a single lumen. In one whole 
mount several faecal pellets lying one on top of the other 
were seen within the siphon and in one series of sections two 
faecal pellets one in the dorsal half and one in the ventral half 
of the siphonal lumen were seen. The gill axes attach laterally 
close to the ventral margin of the siphon, thus any inhalent 
componant is probably restricted to the ventral margin. A 
large siphonal tentacle originates from a pocket in the sipho- 
nal embay ment at the base of the siphon, usually on the left 
side. A small secondary muscular mantle fold marks the inner 
limit of the feeding aperture which in life must extend beyond 
the shell margin as a pair of flaps. Here the inner mantle lobe 
is increased in thickness and width and in the preserved 
contracted state is much folded. The epithelium on the 
ventral side of the secondary muscular fold, on the dorsal side 
of the muscular fold, as well as the epithelium between the 
two, is well supplied with acidophilic gland cells. The gland 
cells within the epithelium between the folds extend anteri- 
orly beyond the limit of the feeding aperture for a short 
distance. The anterior sense organ is well-developed. Over it 
the middle sensory lobe forms a long thin flap which is 
well-supplied with glandular epithelial cells. The adductor 
muscles are large, approximately equal in size with the 'quick' 
and 'catch' parts clearly visible. The anterior adductor if 
anything is slightly the larger, it is 'crescent'-shaped in cross 
section while the posterior muscle is approximately circular. 
The gills lie comparatively ventral in position within the 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



49 




Fig. 71 Yoldiella 
curta. a, lateral 
external and 
internal view of 
left valve of the 
type specimen of 
Y. curta (USNM 
No.38457) and b, 
the lateral 
external and 
internal view of 
the right valve of 
the type specimen 
of Y. miniscula 
(USNM No. 
38415). Specimens 
from the U.S. Fish 
Commission Sta. 
2084 North 
America Basin. 
(Scale =1.0 mm). 



mantle cavity. The outer and inner demibranchs are attached 
to the mantle and body respectively by tissue junctions. 
Depending on the size of the individual there are 11-16 
alternating gill plates. The labial palps are moderately large, 
extending approximately 1/3 across the body and have 
between 13-19 wide ridges on their inner faces. 

The foot is large and well-developed. A large byssal gland 
is present, with little obvious internal structure as seen in 
whole mounts. At the point where the gland opens to the 
exterior the surrounding tissue contains acidophilic gland and 
basiphilic cells. As in other species of Yoldiella there is a 
broad band of posterior retractor muscles. The latero- 
posterior retractor muscle is inserted ventrally on lateral body 
wall. There are three major pairs of anterior pedal retractor 
muscles which, from the neck of the foot, pass to either side 
of the oesophagus and insert on the shell posterior to the 
anterior adductor muscle. Another smaller pair of anterior 
retractor muscles insert immediately posterior to the anterior 
adductor and pass within the ventral visceral margin at 
epithelia to the region of the mouth (Fig. 76b). Posterior to 
these a second pair of muscles pass vertically from the dorsal 
shell margin to the labial palps. 

The cerebral ganglia are relatively large, as are the 
elongate-oval pedal ganglia. The visceral ganglia are smaller, 
cylindrical and lie close to the antero-ventral margin of the 
posterior adductor muscle. 

The mouth is a short distance posterior to the anterior 
adductor muscle. The oesophagus curves dorsally and anteri- 
orly before turning posteriorly to enter the stomach approxi- 
mately midway on the left side of the anterior face. No 
sorting ridges are visible externally on the right side of the 
stomach. There is a prominent gastric tooth at the left 
antero-dorsal edge of the gastric shield. The latter extends 
posteriorly over the left, the dorsal and part of the right wall. 
The style sac is small, narrow and penetrates the foot to level 
of pedal ganglia. The digestive diverticula are extensive 
occurring on the right and left sides of the body and anterior 
to the stomch. Fine material was observed in the lumen of the 
left digestive diverticulum. A duct from the left side opens 
into the stomach below the gastric tooth. The course of the 
two other ducts are less clear, but from the evidence of other 
species they probably open into the stomach anteriorly close 
to the oesophagus. The hind gut sweeps across the ventral 




Fig. 72 Yoldiella curta. a, lateral view from right side of shell, 
detail of the hinge-plate of a right valve and dorsal view of a shell 
from U.S. Fish Commission Sta. 2073 North America Basin, 
compared with b, a lateral view of a shell from the left side and 
detail of the hinge-plate of a right valve from Sta. Polygas DS 25 
West European Basin. (Scale = 1.0 mm). 

right side of the viscera to the anterior adductor muscle, 
where it crosses to the left side of the body to form a single 
loop before returning to the right alongside the outward 



50 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 73 Yoldiella curta. Outlines of shells of a similar size to show 
intrapopulation differences in shape. Specimens from Sta. BG IV 
DS 86 West European Bain. (Scale =1.0 mm). 



50-, 



W/L 



30 J 
80-i 



H/L . 



60 

60- 

50- 



PL/TL 



• • •» > 



1 r 

2 3 

Length (mm) 



Fig. 74 Yoldiella curta. Variation in the ratios of height H/L, width 
W/L and postero-umbonal length PL/TL to length against length 
of a sample from Sta. INCAL CP 01 West European Basin. 




Fig. 75 Yoldiella curta. Outlines of shells from the right side to 
show change in shape with growth. Specimens from Sta. BG I DS 
13 West European Basin. (Scale = 1.0 mm). 

section of the mid dorsal margin of the body and from there 
to the anus. A shallow typhlosole is present along the length 
of the hind gut. Occasional aberrent specimens were 
recorded with an extra length of gut being accommodated 
within the general pattern (see Fig. 75). 

The kidney is well-developed. There is a large pericardial 
cavity but the heart is relatively small with few muscle fibres 
in the wall of the ventricle. Gonads occur dorsally from the 
anterior adductor muscle to just posterior to the stomach and 
in the anterior part of the body internal to the digestive 
diverticula and hind gut. The sexes are separate. In one 
sectioned female (2.3 mm) 27 ova were counted and in other 
specimens (1.8 and 2.1 mm) 69 and 70 ova were recorded 
respectively. The maximum dimension was 108 p.m. 

This is one of a few deep-water specimens which were 
brought to the surface alive and from which it was posible to 
make some observations on the ciliary currents of the mantle 
and the contained organs. The ciliary sorting mechanisms of 
the gills, palps, mantle and body were found to be similar to 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



51 



those described by Stasek (1965) for Yoldia ensifera. 

The ciliation on the frontal surface of the gill plates is 
axially directed, there those on the posterior 2/3rds of the axis 
move anteriorly and those on the anterior l/3rd move poste- 
riorly. Particles thus accumulate at a point which is close to 
where the palp proboscides join the dorsal palp surface and 
they are accepted onto the palp. The palp ridges sort in the 
manner described by Stasek (1965). Rejected particles arrive 
at the posterior-ventral margin of the palp. A main rejection 
tract at the mantle edge to the inside of the muscular fold 
carries these particles to a point of collection at the ventral 
edge of the feeding aperture. Particles on the body eventually 
pass to the dorsal margin of the palps and join with those 
from the gills. 

Hydroids were present on the shell margins of a number of 
specimens. 

Yoldiella perplexa (new species) 

Type locality. R.V. Knorr Sta. 299, Guyana Basin, 

! 29.2.1972, 7°55.1'N, 54°42.0'W, Epibenthic Trawl, 
1912-2076 m. 

Type specimen. Holotype BM(NH) 1992031, Paratypes: in 
collection held by J. A. Allen. 






Fig. 76 Yoldiella curta. Lateral views from the right and left sides 
of the internal morphology of a specimen from Sta. BG VI DS 71 
West European Basin. (Scale = 1.0 mm). For identification of the 
parts see Fig. 34. 



Fig. 77 Yoldiella perplexa. Lateral view of shell from the right 
side, lateral internal view of a right valve to show detail of 
hinge-plate and a dorsal view of a shell. Specimens from Sta. 299 
Guyana Basin. (Scale = 1.0 mm). 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



GUYANA BASIN 

Knorr 25 293 2456- 22 8°58.0'N 54°04.3'W ES 27.2.72 

1518 
299 1942- 82 7°55.1'N 54°42.0'W ES 29.2.72 

2076 



Recorded from the lower slope of the Guyana Basin. Depth 
range: 1456-2076 m. 

Shell description (Fig. 77). Shell small, ovate, moderately 
inflated, inequilateral, smooth with some fine irregularly 
spaced concentric lines at ventral margin, periostracum pale 
yellow; umbos moderately developed, slightly raised, 
inwardly directed anterior to midline; proximal dorsal margin 
straight in small specimens, slightly convex in larger, antero- 
dorsal margin curves gradually to wide anterior margin, 
dorsal part slightly more convex than ventral, ventral margin 
deeply convex, postero-dorsal margin slopes gradually to 
steeply rounded posterior margin, postero-ventral margin 
relatively straight and in some specimens very slightly sinous; 
hinge plate moderately broad, not narrow below umbo, hinge 
teeth strong, few in number, 6 anterior and 6 posterior in 
individual 2.6 mm; ligament amphidetic, moderate in size, 
not extending to ventral edge of hinge plate, round in lateral 



52 




Fig. 78 Yoldiella perplexa. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 299 Guyana Basin. 
(Scale = 1.0 mm). For identification of parts see Fig. 34. 

view with little external periostracal extension anterior and 
posterior to the umbo. 

Prodissoconch length: 177 (xm. Maximum recorded shell 
length: 3.11 mm. 

Internal morphology (Fig. 78). The combined siphons 
are well-developed. There is a long thin siphonal tentacle 
attached to the left ventral side of a moderately deep siphonal 
embayment. The anterior sense organ is well-developed. The 
adductor muscles are relatively large; the anterior is bean- 
shaped and slightly larger than the posterior and which is 
more round. 

The gills bear up to 16 alternating plates which are distant 
from the internal limit of the siphons and to which they are 
joined by long extended axes. The labial palps are relatively 
small and extend approximately 1/4 distance across body. 
There are up to 13 palp ridges on the inner face. The palp 
proboscides are moderately well-developed. 

The foot is also well-developed and anterior in position in 
preserved specimens. There is a small byssal gland and the 
pedal ganglia dorsal to the gland are also small. The visceral 
ganglia are slender and elongate while the cerebral ganglia 
are slightly larger and more 'club'-shaped. The stomach and 
style sac are large. The hind gut describes a shallow single 
loop to the right side of the body. No gonads were seen in the 
whole mounts. 

Y. perplexa is characterized by a rounded high shell which 
has a slightly sinuous postero-ventral shell margin. Unlike 
other high rounded species such a Y. americana and Y. 
subcircularis it has a simple and not particularly extensive 
hind gut loop to the right and thus has characters intermedi- 
ate between Y. lucida or Y. obesa and species such as Y. 
subcircularis. 

Yoldiella americana (new species) 

Type locality. R.V. Chain Sta. 84, North America Basin, 
4.7.1965, 36°24.4'N, 67°56.0'W, Epibenthic Trawl, 4749 m. 

Type specimen. Holotype BM(NH) 1992032, Paratypes: in 
collection held by J. A. Allen. 





J. A. ALLEN, 


H.L. SANDERS AND F. HANNAH 


Material. 














Cruise 


Sta 


Depth 


No 


Lat 


Long 


Gear Date 






(m) 












NORTH AMERICA BASIN 










Atlantis II 

12 
Chain 50 


70 


4680 


190 


36°23.0'N 


67°58.0'W 


ET 


23. 8.64 


77 


3806 


1 


38°00.7'N 


69°16.0"W 


et 


30. 6.65 




80 


4970 


75 


34°49.8'N 


66°34.0"W 


ET 


2. 7.65 




81 


5042 


9 


34°41.0'N 


66°28.0'W 


ET 


2. 7.65 




83 


5000 


4 


34°46.5'N 


66°30.0'W 


ET 


3. 7.65 




84 


4749 


235 


36°24.4'N 


67°56.0'W 


ET 


4. 7.65 




85 


3834 


4 


37°59.2'N 


69°26.2'W 


ET 


5. 7.65 




86 


3843 


268 


37°59.0'N 


69°18.5'W 


ET 


5. 7.65 


Atlantis II 


92 


4694 


3 


36°20.0'N 


67°56.0'W 


ET 


13.12.65 


17 


93 


5003 


6 


34°39.0'N 


66°26.0'W 


ET 


14.12.65 


Atlantis II 


121 


4800 


66 


35°50.0'N 


65°11.0'W 


ET 


21. 8.66 


24 


122 


4833 


25 


34°50.0'N 
35°52.0'N 


64°57.5'W 
64°58.0'W 


ET 


21. 8.66 




123 


4853 


94 


37°29.0'N 


64°14.0'W 


ET 


22. 9.66 




124 


4862 


76 


37°26.0'N 
37°25.0'N 


63°59.5'W 
63°58.0'W 


ET 


22. 8.66 




125 


4825 


37 


37°24.0'N 
37°26.0'N 


65°54.0"W 
65°50.0"W 


ET 


23. 8.66 


Atlantis II 


175 


4667- 


145 


36°36.0'N 


68°29.0'W 


ES 


29.11.67 


40 




4693 




36°36.0'N 


68°31. 0'W 






Chain 106 


330 


4632 


243 


50°43.5'N 
50°43.4'N 


17°51.7'W 
17°52.9'W 


ES 


24. 8.72 




331 


4793 


10 


41°13.0'N 
41°13.2'N 


41°36.7'W 
41°38.7'W 


ES 


29. 8.72 



ARGENTINE BASIN 

Atlantis II 242 4382- 8 38°16.9'S 
60 4402 

247 5208- 293 43°33.0'S 

5223 
252 4435 1 38°29.8'S 



51°56.1'W ES 13. 3.71 
48°58.1'W ES 17. 3.71 
52°09.1'W ES 22. 3.71 



GUYANA BASIN 

Knorr25 287 4980- 12 

4034 

288 4417- 45 

4429 

Biovema DS03 5150 3 

DS05 5100 28 

CO04 5100 1 

DS09 5875 1 

DS11 5867 2 



13°16 
13°15 
11°02 
11°03 
10°47 
10°47 
10°45 
10°46 
10°45 
10°45 
11°36 
11°37 
11°37 
11°37 



0'N 
8'N 
2'N 
8'N 
l'N 
.l'N 
9'N 
8'N 
9'N 
9'N 
5'N 
l'N 
5'N 
6'N 



54°52.2'W 
54°53. l'W 
55°05.5'W 
55°04.8'W 
42°40.7'W 
42°40.3'W 
42-40.2'W 
42°39.8'W 
42°40.2'W 
42°39.3"W 
32-51. 8 "W 
32°51. 3' W 
32°43.8'W 
32°52.8'W 



ES 24. 2.72 



ES 25. 2.72 



DS 16.11.77 



DS 18.11.77 



CP 18.11.77 



DS 25.11.77 



DS 26.11.77 



SIERRA LEONE BASIN 

Atlantis II 139 2099- 

31 2187 



1 10°33.0'N 17°53.0'W ES 4. 2.62 



Y. americana is found mainly in the deep western Atlantic 
with a few records to east of the Atlantic Ridge at the western 
edge of the Sierra Leone Basin. Otherwise the species is 
recorded from the North America, Guyana and Argentine 
Basins. Depth range: 2099-5867 m. 

Shell description (Fig. 79). Shell small, ovate, moderately 
inflated, approximately equilateral; umbos moderately 
raised, inwardly directed; dorsal margin slightly convex, 
antero-dorsal margin slopes evenly to join broad curve of 
anterior margin, ventral margin more convex posteriorly, 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



53 




Fig. 79 Yoldiella americana. Lateral view of shell from the right 
side, lateral internal view of a left valve, enlarged view of a 
hinge-plate of a left valve and a dorsal view of the shells. 
Specimens from Sta. 80, North America Basin. (Scale = 1.0 mm). 



50 



W/L 



30 J 
80 



H/L * * 



T 1 * A 



PL/TL 








* i*\ 


»« *" 


■ 


• a • 


«* 









60 
60 

50 



Length (mm) 

ig. 80 Yoldiella americana. Variation in ratio of height H/L, 
width W/L and postero-umbonal length PL/TL to length against 
length of subsamples from Sta. Biovema DS 05, Cape Verde 
Basin (closed circles) and from Sta. 247 Argentine Basin (open 
triangles). 

posterior margin rounded or with slight angulation forming 
slight subrostrum; hinge plate moderately strong, long strong 
:hevron-shaped teeth, equal numbers on anterior and poste- 
"ior plates, 14/14 in a specimen 2.44 mm total length; 
igament amphidetic, small, rectangular in shape, small poste- 



rior external extension of fused periostracum. 

Prodissoconch length: 187 |xm. Maximum recorded shell 
length: 2.5 mm. 

There is little change in the posterior umbonal length/total 
length ratio or the height/length ratio with increasing size, 
however, individuals tend to become more tumid with 
increasing length. The width/length ratio is the most variable 
feature when comparing populations from different areas 
(Fig. 80). Thus, specimens from the west Atlantic are rela- 
tively wider than those from the the east Atlantic although in 
lateral view (Fig. 81) and in internal anatomy they differ 
little. Populations are remarkably different in their size 
range. This is probably indicative of single massive successful 
spatfalls at different times (Fig. 82). 

Internal morphology (Fig. 83). The anterior sense organ 
is moderately well-developed. The siphons are combined, 
with the inhalent siphon open at the ventral edge. A siphonal 
tentacle originates from the base of the siphonal embayment, 
either on the right or the left side. There is a feeding aperture 
ventral to the siphons. Anterior to this the inner muscular 
lobe is enlarged convoluted and heavily ciliated. The adduc- 






Fig. 81 Yoldiella americana. Outlines of shells from the right side 
to show change in shape with growth of specimens from Sta. 
Biovema DS 05 Cape Verde Basin (left) compared with 
specimens from Sta. 247 Argentine Basin. (Scale =1.0 mm). 



54 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



tor muscles are relatively small and elongate and approxi- 
mately equal in size. The gills are well-developed. The exact 
number of gill plates is difficult to determine but at least 16 
are present in the largest specimen. The labial palps are 
relatively large with up to 17 ridges on the inner face and with 
long palp proboscides. The foot is elongate with a relatively 
narrow neck. Many subepithelial gland cells open on to the 
sole of the foot. There is a relatively large byssal gland in the 
heel. A small papilla is present immediately posterior to the 
aperture of the byssal gland. The cerebral and visceral ganglia 
are 'club'-shaped and of moderate size. The pedal ganglia, in 
the neck of the foot, are large and elongate. 

The hind gut passes from the style sac to the left side of the 
body and forms a loop then crosses to the right side where it 
forms a similar loop before passing postero-dorsally to the 
anus. The point of crossover from left to right is ventral to the 
ligament or slightly posterior to it. A small typhlosole is 
present along the length of the gut. 

The sexes are separate. From whole mounts, it appears 
that the ovaries contain relatively few large ova. The testes 
occupy a large part of the anterior half of the body with the 
digestive diverticula dorsal to them. 

Y. americana has a similar rounded shape to Y. perplexa 
although without the slight sinuous postero-ventral margin of 
the latter species. Y. americana is the only species taken with 
a single hind gut loop to the right and left of the body. 

Yoldiella subcircularis (Odhner 1960) 

Portlandia (Yoldiella) subcircularis Odhner 1960, p. 369, pi. 
1, Fig. 1. 

Type locality. Swedish Deep-Sea Expedition, Sta. 373, 
North America Basin, collected by R.V. Albatross, 
24.8.1948, 28°25'N, 61°05'W - 28°05'N, 60°49'W, 
5,500-5,987 m. 



6CH 



3 40- 



20- 



1 2 

Length (mm) 

Fig. 82 Yoldiella americana. Length frequency histogram of a 
sample from Sta. 84, North America Basin. 





Fig. 83 Yoldiella americana. Lateral views from right and left sides 
of the internal morphology of a specimen from Sta. 84, North 
America Basin. (Scale = 1.0 mm). For identification of parts see 
Fig. 34. 

Type specimen. Holotype: Swedish Museum of Natural His- 
tory, Stockholm. 



Material. 












Cruise 


Sta DepthNo 
(m) 


Lat 


Long 


Gear Date 


WEST EUROPEAN BASIN 










Jean Charcot DS20 4226 


7 


47°33.0'N 


9°36.7'W 


DS 


24.10.72 


(Poly gas) 


DS21 4190 


1 


47°31.5'N 


9°40'7'W 


DS 


24.10.72 




DS22 4144 


4 


47°34.1'N 


9°38.4'W 


DS 


25.10.72 


(Biogas IV) 


DS54 4659 


2 


46°31.1'N 


10°29.2'W 


DS 


21. 2.74 




DS55 4125 


7 


47°34.9'N 


9°40.9'W 


DS 


22. 2.74 


(Biogas V) 


S68 4550 


1 


46°26.7'N 


10°23.9'W 


DS 


19. 6.74 


(Biogas VI) 


DS75 3250 


1 


47°28.1'N 


9°07.8'W 


DS 


22.10.74 




DS76 4228 


29+1 


v 47°34.8'N 


9°33.3'W 


DS 


23.10.74 




DS77 4240 


13+2v 47°31.8'N 


9°34.6'W 


DS 


24.10.74 




DS78 4706 


4 


46°31.2'N 


10°23.8'W 


DS 


25.10.74 




DS79 4715 


13 


46°30.4'N 


10°27.1'W 


DS 


26.10.74 




DS80 4720 


4 


46°29.5'N 


10°29.5'W 


DS 


27.10.74 




DS81 4715 


1 


46°28.3'N 


10°24.6'W 


DS 


27.10.74 


Jean Charcot QS02 4829 


2 


48°19.2'N 


15°15.7'W 


OS 


2. 8.76 


(Incal) 


QS05 4296- 
4248 


1 


47°31.3'N 
- 47°32.2'N 


9°34.6'W 
9°34.7'W 


OS 


7. 8.76 




QS06 4316 


6 


46°27.3'N 
- 47°27.9'N 


9°36.2'W 
9°36.0'W 


OS 


9. 8.76 




QS07 4249 


15 


47°31.8'N 
- 47°31.3'N 


9°34.3'W 
9°34.3'W 


OS 


10.8.76 




QS08 4327 


5 


47°29.8'N 
- 47°29.5'N 


9°39.2'W 
9°38.8'W 


OS 


11. 8.76 




WS03 4829 


10 


48°19.2'N 
- 48°19.1'N 


15°23.3'W 
15°22.5'W 


WS 


1. 8.76 




WS07 4281 


4 


47°30.6'N 

- 47°31.2'N 


9°37.1'W 

9°35.7'W 


WS 


7. 8.76 




WS08 4287 


11 


47°30.5'N 


9°33.7'W 


WS 


9. 8.76 




WS09 4277 


3 


47°28.8'N 
- 47°27.9'N 


9°34.0'W 


WS 


10. 8.76 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



55 





WS 10 4354 


10 


47°27.3'N 
- 47°18.2'N 


9°39.9'W 


WS 


11. 8.76 


Jean Charcot DS11 4823 


1 


48°18.8'N 


15°11.5'W 


DS 


1. 8.76 


(Incal) 






- 48°18.6'N 


15°12.0'W 








DS14 4254- 


3 


47°32.6'N 


9°35.7'W 


DS 


7. 8.76 




4248 




- 47°32.6'N 


9°35.1'W 








DS15 4268 


12+2v 47°29.8'N 


9°33.4'W 


DS 


9. 8.76 








- 47°30.3'N 


9°33.4'W 








CPU 4823 


1 


48°20.4'N 
- 48°21.2'N 


15°14.6'W 
15°13.7'W 


CP 


1. 8.76 


Chain 106 


330 4632 


8 


50°43.5'N 
- 50°43.4'N 


51°07.0'W 
51°09.0'W 


ES 


29. 8.72 


CANARIES BASIN 












Discovery 


6714 3301 


3 


27°13.0'N 


15°41.0'W 


ES 


20. 3.68 


GUYANA BASIN 












Knorr 25 


287 4980- 
4934 


5 


13°16.0'N 


54°52.2'W 


ES 


24. 2.72 




288 4417- 


64 


11°02.2'N 


55°05.5'W 


ES 


25. 2.72 




4429 












Jean Charcot DS03 5150 


1 


10°47.1'N 


42°40.7'W 


DS 


16.11.77 


(Biovema) 






- 10°47.1'N 


42°40.3'W 








DS05 5100 


6 


10°45.9'N 
- 10°46.0'N 


42°40.2'W 
42°39.8'W 


DS 


18.11.77 




CP04 5100 


1 


10°45.9'N 
- 10°45.9'N 


42°40.2'W 
42°39.3'W 


CP 


18.11.77 


CAPE BASIN 












Jean Charcot DS05 4560 


3 


33°20.5'S 


2°34.0'E 


DS 


30.12.78 


(Walvis) 


DS06 4585 


7 


33°24.5'S 


2°32.0'W 


DS 


31.12.78 




DS07 5100 


20 


26°59.7'S 


1°07.1'E 


DS 


1. 1.79 




DS08 5225 


3 


26°59.6'S 


1°07.3'E 


DS 


5. 1.79 




DS09 5220 


15 


26°59.9'S 


1°06.7'E 


DS 


6. 1.79 


NORTH AMERICA BASIN 










Atlantis II 

12 
Chain 50 


70 4680 


1 


36°23.0'N 


67°58.9'W 


ET 


23. 8.64 


78 3828 


2 


38°00.0'N 


69°18.7'W 


ET 


30. 6.65 




80 4970 


45 


34°49.8'N 


66°34.0'W 


ET 


2. 7.65 




81 5042 


14 


34°41.0'N 


66°28.0'W 


ET 


2. 7.65 




83 5000 


2 


34°46.5'N 


66°30.0'W 


ET 


3. 7.65 




85 3834 


8 


37°59.2'N 


69°26.2'W 


ET 


5. 7.65 


Atlantis II 

17 
Atlantis II 


92 4694 


3 


36°20.0'N 


67°56.0'W 


ET 


13.12.65 


93 5007 


23 


34°39.0'N 


66°26.0"W 


ET 


14.12.65 


24 


121 4800 


2 


35°50.0'N 


65°11.0'W 


ET 


21. 8.66 


Atlantis II 


175 4667- 


2 


36°36.0'N 


68°29.0'W 


ES 


29.11.67 


40 


4693 



























This is a true abyssal species found only in the deepest part of 
the Basins and, except for the Argentine & Norwegian Basins 
is widely distributed throughout the Atlantic. Depth range: 
3250-5225 m. 

Shell description (Figs. 84 & 85). Shell small, moderately 
thick, oval, inflated, inequilateral, posterior margin slightly 
produced; surface with very fine irregular concentric lines, 
fine radial striae present in some specimens, dorsal area 
between umbo and posterior margin furrowed; umbos raised 
slightly, orthogyrate; dorsal margin proximally straight on 
either side of umbo, distally antero-dorsal margin joins 
rounded anterior margin in broad curve which continues to 
ventral margin, more convex posteriorly, distal postero- 
dorsal margin curves more gradually to produce slightly 
drawn out posterior margin, limit of posterior margin supra- 
medial; hinge plate moderately broad, long, slightly curved, 
up to 10 small 'V'-shaped, chevron teeth on each side of 
ligament; ligament amphidetic, small, 'goblet'-shaped, small 
external extension of fused periostracum on either side of 
umbo, small chondrophore present. 

Prodissoconch length: 146-187 u.m. Maximum recorded 
shell length 4.4 mm. 

The description of Portlandia (Y) subcircularis (Odhner, 
1960) agrees well with that presented above. 

With increasing length, the posterior part of the shell 
becomes slightly more extended and at the same time the 
postero-dorsal margin becomes more smoothly curved (Figs. 
85 & 86). The width to length ratio also increases with 
increasing size, but little proportionate change occurs in the 
height to length ratio although this varies in individuals 
between 0.72 and 0.84. The height/length ratios are the 
highest recorded for any species of Yoldiella. In some larger 
specimens the dorsal margin immediately anterior and poste- 
rior to the umbos may become slightly concave and as a result 
a small, shallow lunule and escutcheon may be formed. 
Comparison of specimens from the different Basins show that 
northerly (W. European) and southerly (Angola) populations 
in the eastern Atlantic are similar in form as too are the North 





Fig. 84 Yoldiella subcircularis. 
Lateral view of a shell from the 
right side and a right valve to show 
the detail of the hinge-plate. 
Specimens from Sta. 285 Guyana 
Basin and Sta. 93 North Atlantic 
Basin respectively. (Scale = 1.0 
mm). 



56 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 85 Yoldiella subcircularis . Outlines of shells from the right 
side to show variation in shape. Specimens taken from Sta. BG 
VI DS 76, West European Basin. (Scale = 1.0 mm). 



50 
40 



W\L 



■ • X. ■ "j 



America specimens. In contrast the small number of speci- 
mens from the Guyana Basin differ slightly in having a lower 
height/length ratio (significant at the 0.1 level). 



Internal morphology (Figs. 87 & 88). In Y. subcircularis 
the volume of the mantle cavity is large compared with that of 
the body. A well-developed sense organ lies at the far 
anterior margin. The siphons are combined and the inhalent 
siphon is shorter than the exhalent and is open ventrally. 
Both siphons are thin-walled and a pair of lateral haemoco- 
eles are present in the junction between them. There is a 
moderately large siphonal tentacle, most frequently found on 
the left side. The feeding aperture is well-developed with 
areas of glandular mantle epithelium on each side which are 
probably extended in life as paired, broad flaps. For some 
distance anterior to these, the inner muscular lobe is particu- 
larly well-ciliated and it may be that the feeding area either is 
separated from the pedal gape by a ciliary junction or it is the 
region where pseudofaeces are formed. The adductor 
muscles are small, approximately equal in size, oblong in 
shape and lie close to the dorsal and anterior and posterior 
mantle margins respectively. 

The gill plates are relatively few in number (18 in a 
specimen 3.0 mm). Tissue junctions join the demibranchs to 
the mantle dorsally. The gill plates are particularly muscular 




i 



80 
70 



*j.A::V'i£ *■ '■ 



H\L 



60- 
50- 


PL\TL 


■ 


••I"..* 


• 
• 


• 


:.-.y*-. 


*■■.. 


■ 
■ 


■ 




i 




i 






i 




1 





Length(mm) 

Fig. 86 Yoldiella subcircularis. Variation in ratios of height H/L, 
width W/L and postero-umbonal length PL/TL to length against 
length of subsamples from Sta. BG DS 76, West European Basin 
(closed circles) and Sta. Walvis QS 07, Cape Basin (closed 
squares). 




Fig. 87 Yoldiella subcircularis. Lateral views from right and left 
sides of the internal morphology of a specimen from Sta. 80 North 
America Basin. (Scale =1.0 mm). For identification of parts see 
Fig. 34. 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



57 



and well-developed. The labial palps are large, with up to 32 
closely spaced ridges on each inner face. In some of the 
largest specimens (> 3.3 mm) the anterior part of the palps 
are frequently folded in on themselves. The palp proboscides 
are relatively small and slender. The foot is conspicuous, 
being long and thin, with a much extended narrow neck and a 
long divided papillate sole. Gland cells are present along the 
ventral part of the sole and surrounding the aperture of a 
large byssal gland. Pedal retractor muscles are less conspicu- 
ous in this species than in others described here. The central 
haemocoele of the foot is extensive. The cerebral and visceral 
ganglia are relatively small, circular in transverse vertical 
cross-section. The visceral ganglia are some distance anterior 
to the posterior adductor muscle. The pedal ganglia lie at the 
dorsal limit of the extended neck of the foot close to its 
junction with the body, they are large and elongate with large 
associated statocysts dorsal to them. 

The mouth is displaced a short distance posteriorly from 
the anterior adductor muscle. The stomach and style sac are 
moderately large. Two broad sorting ridges can be seen on 
the right anterior wall of the stomach. A prominent gastric 
tooth is present on the left dorsal wall and posterior to it the 
gastric shield extends over the left and most of the right walls 
of the stomach. The major typhlosole extends along the right 
side of the stomach. The digestive diverticula lie either side 
and anterior to the stomach. The duct of the right digestive 
diverticulum curves dorsally over the hind gut and enters the 
stomach on the right anterior dorsal wall. A duct from one 
left diverticulum enters the stomach far anterior on the left 
dorsal side, and immediately posterior to it, a short duct from 
a second left diverticulum enters the stomach, ventral to the 
gastric tooth. Material similar to that in the stomach was 
present in the lumen of the latter diverticulum, but this could 
possibly have resulted from tissue contraction following fixa- 
tion. The style sac is relatively large and extends into the 
dorsal part of the foot. The hind gut has a shallow typhlosole 
along its entire length, the impression of which can be seen on 
extruded faecal pellets. The hind gut is arranged in two loops 
on each side of the body. These are usually visible through 





Fig. 88 Yoldiella subcircularis . Dorsal view of the hind gut of a 
specimen from Sta. 80 North America Basin and a diagrammatic 
view of the course of the hind gut as seen from the left side. 
(Scale = 1.0 mm). 



the shell antero-dorsally. There is also a double vertical 
extension of the hind gut deep into the foot. Thus, design 
advantage is taken of the exceptional length of the neck of the 
foot to accommodate a significant part of the greatly 
extended hind gut. 

The sexes are separate. Sectioned specimens larger than 
2.8 mm had maturing gonads. The number of ova ranged 
from 37 (2.80 mm) to approximately 140 (2.91 mm) with a 
maximum ovum diameter of 132 u.m and 156 um respectively. 
The gonads overlie the lateral and dorsal sides of the viscera. 
Mature females were present in February, June, August and 
October samples from the West European Basin. In two 
specimens from (Sta. DS76, Sta. DS79 respectively both 2.91 
mm total length), eggs were partially shed into the mantle 
cavity and had a maximum dimension of 156 u.m. Neverthe- 
less, there is no evidence to show that eggs are retained and 
incubated within the mantle cavity. 

Although the kidney is relatively small, it extends forward 
on either side of the stomach for a short distance. 



Yoldiella biguttata (new species) 

Type locality. R.V. Knorr Cruise 25, Sta. 299, Guyana 
Basin, 29.2.1972, 7°55.1'N, 55°42.0'W, Epibenthic Trawl, 
1942-2076 m. 

Type specimen. Holotype: BM(NH) 1992029. Paratypes: in 
collection held by J. A. Allen. 



Material. 










Cruise Sta 


Depth No 

(m) 


Lat 


Long 


Gear Date 


BRAZIL BASIN 
Atlantis II 167 
31 


943- 5 
1007 


7°58.0'S 
- 7°50.0'S 


34°17.0'W 
34°17.0'W 


ES 20.2.67 



ARGENTINE BASIN 

Atlantis II 245 2707 
60 



36°55.7'S 53°01.4'W ES 14.3.71 



GUYANA BASIN 

Knorr 25 293 1456- 13 8°58.0'N 54°04.3'W ES 27.2.72 

1518 
295 1000- 2 8°04.2'N 54°21.3"W ES 28.2.72 

1022 
299 1942- 74 7°55.1'N 55°42.0"W ES 29.2.72 

2076 
301 2487- 44 8°12.4'N 55°50.2'W ES 29.2.72 

2500 
303 2849- 4 8°28.8'N 56°04.5'W ES 1. 3.72 

1853 

Y. biguttata is distributed off the coast of eastern South 
America at mid slope to abyssal depths in the Argentine, 
Brazil and Guyana Basins. Depth range: 943-2853 m. 

Shell description (Fig. 89). Shell small, inflated, equilat- 
eral, fine concentric striae; umbos posterior to midline, 
slightly raised, moderately large, inwardly directed; dorsal 
margin raised, sharp-edged, particularly so anterior to umbo, 
dorsal margin close to umbo straight, proximal antero-dorsal 
margin curves to broadly rounded anterior margin, the limit 
of which is slightly ventral to the midline, ventral margin 
shallow curve, in some specimens almost straight centrally, 
postero-ventral margin sinuous giving a characteristic oblique 



58 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 89 Yoldiella biguttata. Lateral views 
of shells from the right and left sides and a 
right valve in inner lateral and dorsal view 
to show variation in shape and hinge-plate 
details. Specimens from Sta. 301 and Sta. 
299, Guyana Basin. (Scale = 1.0 mm). 



configuration to shell in lateral view; hinge plate moderately 
shallow, short, reaching no further than inner limit of adduc- 
tor muscles, teeth few, anterior and posterior series either 
equal or with one additional tooth in anterior series (5/6 in 
largest specimen); ligament amphidetic, very large in relation 
to size of shell. 

Shell measurements (mm) & ratios are as follows:- 



Length 


Height 


Width 


H/L 


W/L 


PL/TL 


1.64 


1.24 


0.89 


0.75 


0.54 


0.39 


1.62 


1.12 


0.72 


0.69 


0.44 


0.45 


1.50 


1.07 


0.68 


0.72 


0.45 


0.46 


1.50 


1.08 


0.73 


0.72 


0.49 


0.39 


1.37 


1.02 


0.70 


0.74 


0.51 


0.47 


1.19 


0.81 


0.48 


0.68 


0.40 


0.39 


0.87 


0.62 


0.33 


0.71 


0.38 


0.40 



Prodissoconch length: 198 p.m. Maximum recorded shell 
length: 1.64 mm. 

Internal morphology (Fig. 90). The combined siphon is 
thin-walled and with a single lumen. In that the gill axis joins 
the ventral edge of the siphon the inhalent component can be 
assumed to be largely absent. The siphon is not open ven- 
trally. A single fine, elongate mantle tentacle originates on 
the left ventral inner limit of the moderately deep siphonal 
embayment. An area of secretory cells is present at the base 
of the siphon. Ventral to the siphon is a well-developed 
feeding aperture. The posterior adductor muscle is round in 
cross-section while the anterior is slightly larger and 
'crescent'-shaped. The visceral and cerebral ganglia are well- 
developed and joined by a stout commissure. The cerebral 
ganglia are slightly the larger. The gills have a relatively small 
number of plates (maximum number recorded 9) most of 
which are carried posterior to the foot. Labial palp ridges 
number 14-18, depending on the size of the specimen, and 
are moderately large. The palp proboscides are also moder- 
ately large. The foot papillae contain considerable numbers 




Fig. 90 Yoldiella biguttata. Lateral views from the right and left 
sides of the internal morphology of a specimen from Sta. 299, 
Guyana Basin. (Scale = 1.0 mm). For identification of the parts 
see Fig. 34. 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



59 



of secretory cells. There is a relatively large single posterior 
papilla immeditely posterior to the aperture of the byssal 
gland at the heel of the foot. The gland is large and is 
surrounded by secretory cells. The hind gut is complex with 
twinned loops on each side of the body, with two recurved 
sections immediately anterior to the stomach. The main 
lateral loops of the hind gut cross from one side of the body to 
the other dorsally and immediately posterior to the resilium. 
All the specimens examined had well-developed gonads 
which makes it difficult to determine the exact course of the 
gut, but from sections we are confident that it has a similar 
design to that described for Yoldiella subcircularis . One 
sectioned female (1.63 mm total length) from Sta. 299 has 18 
large ova present (maximum observed dimension 114 p.m). 

Despite the similarity of the internal morphology to that of 
Yoldiella subcircularis the shapes of the shell, hinge and 
ligament are totally different in the two species (p. 55). As we 
point out elsewhere the various types of hind gut morphology 
do not necessarily correlate to a particular characteristic suite 
of shell characters. All that can be said with certainty is that 
the hindgut of Yoldiella biguttata has configuration so far 
found only in the Yoldiellidae and only in species from the 
abyss and abyssal rise. 



Yoldiella ovata (new species) 

TYPE LOCALITY. R.V. Knorr Cruise 25, Sta. 300, Guyana 
Basin, 29.2.1972, 8°14.2'N, 55°53.5'W, Anchor Dredge, 
2524-2542 m. 

Type specimen. Holotype: BM(NH) 1992035. Paratypes: in 
collection held by J. A. Allen. 



Material. 




Fig. 91 Yoldiella ovata. Lateral views of a shell from the left side 
and dorsally and an inner view of a left valve to show detail of the 
hinge-plate. Specimens taken from Sta. 300, Guyana Basin. 
(Scale =1.0 mm). 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



GUYANA BASIN 

Knorr 25 300 2524- 208 8°14.2'N 55°53.5"W AD 29.2.72 
2542 
301 2487- 324 8°12.4'N 55°50.2"W ES 29.2.72 

2500 
303 2842- 13 8°28.8'N 56°04.5'W ES 1 .3.72 
2853 

Restricted to the abyssal rise of the Guyana Basin. Depth 
range: 2487-2853 m. 

Shell description (Figs. 91 & 92). Shell small, ovate, 
moderately inflated, inequilateral, transparent, dorso- 
lateral^ smooth, ventrally, with very fine concentric lines 
forming ridges; umbos slightly anterior of midline, moder- 
ately inflated, orthogyrate; dorsal margin slightly convex, 
antero-dorsal and postero-dorsal margins with similar curva- 




Fig. 92 Yoldiella ovata. Outlines of shells from the right side to 
show change in shape with growth of specimens from Sta. 300, 
Guyana Basin. (Scale = 1.0 mm). 



60 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



ture, ventral margin smoothly curved, posterior margin 
somewhat more convex than anterior and very slightly 
extended, anterior and posterior margins broad, rounded; 
hinge plate elongate, moderately wide except below umbo 
where narrow, moderately strong, acute taxodont teeth, 7 in 
anterior and 8 in posterior series in specimen 2.3 mm; 
ligament internal, amphidetic, slightly elongate, barely 
extends below hinge plate. 

Prodissoconch length: 172 |xm. Maximum recorded shell 
length: 2.9 mm. 

Internal morphology (Fig. 94). The inhalent and exhal- 
ent siphons are combined, the inhalent is open along its 
ventral margin. The siphonal tentacle is either to the right or 
left. There is a feeding aperture and anterior to it a heavily 
ciliated region of the inner mantle fold. There is a well- 
developed anterior sense organ. The posterior adductor 
muscle is small and oval, the anterior adductor, also oval, is 
approximately twice the size of the posterior. The labial palps 
are moderately large with up to 19 palp ridges and each has a 
long thin palp proboscis. The gill which is small, dorsal in 
position in preserved specimens, has up to 14 plates. The 
visceral and cerebral ganglia are typically 'club'-shaped, the 
visceral being the smaller. The pedal ganglia are moderately 
large, elongate and situated high in the foot. The foot is long 
and thin with deep papillae fringing the sole. A large byssus 
gland is present in the heel. 

The stomach and style sac are small and the latter does not 
penetrate far into the foot. The hind gut forms double loops 
to the left and right of the body, recurring anterior to the 
stomach, thus taking a similar course to Yoldiella subcircu- 
laris and Yoldiella biguttata. A considerable amount of fine 
material was present in the digestive diverticula of the left 
side. The kidneys although moderately well-developed do not 



5CH 
40 

80- 
70- 

60- 
50- 



W\L 



H\L 



PL\TL 



*. » 





Length(mm) 



Fig. 94 Yoldiella ovata. Lateral views from the right and left side 
of the internal morphology of a specimen from Sta. 300, Guyana 
Basin. (Scale = 1.0 mm). For identification of the parts see Fig. 
34. 

penetrate anteriorly into the visceral mass to any great 
extent. The sexes are separate. One sectioned female (2.7 
mm) contained approximately 50 ova with a maximum diam- 
eter of 80 u.m. 

With increasing length, the height/length, width/length and 
particularly the posterior umbonal length/total length ratios 
gradually increase (Fig. 93). 

Yoldiella ovata is closely related to Y. biguttata, but can be 
distinguished by its more ovate outline and not being flat- 
tened at the postero-ventral shell margin. 

Yoldiella insculpta (Jeffreys 1879) 



Fig. 93 Yoldiella ovata. Variation in the ratios of height H/L, 
width W/L and postero-umbonal length PL/TL to length against 
length of subsample from Sta. 300, Guyana Basin. 



Type locality. West of Ireland, H.M.S. Porcupine, 1869, 
Sta. 16, 54°19'N, 11°50'W, 816 fms. 

Type specimen. Holotype: not designated. Lectotype: (here 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



61 



designated) BM(NH) 85.11.5.459. 

Leda insculpta Jeffreys 1879, p. 580, pi. 46, Fig. 5; Dautzen- 
berg 1889, p. 80; Dautzenberg & Fischer 1897, p. 204; 
Locard 1898, p. 355. 

We have examined the material designated as syntypes by 
Waren (1980) and housed in the collections of the U.S. 
National Museum and the Natural History Museum, London. 

Material. 



Cruise Sta Depth No Lat Long 

(m) 



Gear Date 



WEST EUROPEAN BASIN 










La Perle 


DS11 2205 


9+2v 


47°35.5'N 


8°33.7'W 


DS 


8. 8.72 


(Biogas I) 


DS13 2165 


23+6v 47°33.7'N 


8°39.9'W 


DS 


10. 8.72 


Jean Charcot DS15 2246 


5 


47°35.2'N 


8°40. l'W 


DS 


21.10.72 


(Polygas) 


DS16 2325 


1 


47°36.1'N 


8°40.5'W 


DS 


21.10.72 




DS18 2138 


4 


47°31. 2'N 


8°44.9'W 


DS 


22.10.72 


(BiogasII) 


DS31 2183 


4 


47°32.5'N 


9°04. 2 "W 


DS 


19. 4.73 




DS32 2138 


14 


47-32.2'N 


8°05.3"W 


DS 


19. 4.73 


(BiogasIII) 


DS35 2226 


18+8v 47°34.4'N 


8°40.7"W 


DS 


24. 8.73 




DS36 2147 


5 


47°32.7'N 


8°35.6'W 


DS 


24. 8.73 




DS37 2110 


12+ 

54v 

2 


47-31 .8'N 


8°34.6'W 


DS 


24. 8.73 




DS38 2138 


47°32.5'N 


8°35.8'W 


DS 


25. 8.73 


(Biogas IV) 


DS61 2250 


10+2v 47°34.7'N 


8°38.8'W 


DS 


25. 2.74 




DS62 2175 


63 


47°32.8'N 


8°40.0'W 


DS 


26. 2.74 




DS63 2126 


23 + 
lOv 
18+ 
12v 

8+4v 


47°32.8'N 


8°35.0'W 


DS 


26. 2.74 




DS64 2156 


47-29.2'N 


8°30.7'W 


DS 


26. 2.74 




CP01 2245 


47°34.6'N 


8°38.8'W 


CP 


25. 2.74 


(Biogas V) 


DS65 2360 


1 


47°36. l'N 


8°40.5'W 


DS 


15. 6.74 




DS71 2194 


6+2v 


47°34.3'N 


8°33.8'W 


DS 


20.10.74 




DS87 1913 


1 


44 o 05.2'N 


4°19.4'W 


DS 


1.11.74 




CP08 2177 


11+2 


44°33.2'N 


8°38.5'W 


CP 


20.10.74 




CP09 2171 


24+4v 47°33.0'N 


8-44.0'W 


CP 


20.10.74 


Sarsia 


65 1922 


42 


46°15.0'N 


4°50.0'W 


ED 


25.7.67 


CANARIES BASIN 












Discovery 


6701 1934 


1 


27-45.2'N 


14°13.0'W 


ED 


16. 3.68 




6704 2129 


1 


27°44.9'N 


14°25.0"W 


ED 


17. 3.68 




6710 2670 


2 


27-23.6'N 


15°39.6'W 


ED 


19. 3.68 




6714 3301 


2 


27-13.0'N 


15°41.0"W 


ED 


20. 3.68 




Fig. 95 Yoldiella insculpta. Dorsal and lateral view of shell from 
the right side and a lateral view of the hinge-plate of a left valve. 
Specimens from Sta. BG IV DS 62, West European Basin. 
(Scales =1.0 mm). 




Fig. 96 Yoldiella insculpta. Lateral view of shell from the left side 
and an inner view of right valve. Specimens from Sta. 16 and Sta. 
17 Porcupine Expedition, W. of Portugal. (USNM No. 199773). 
(Scale =1.0 mm). 




Fig. 97 Yoldiella insculpta. Outlines of shells from the right side to 
show variation in shape. Specimens from Sta. BG DS 63, West 
European Basin. (Scale = 1.0 mm). 



62 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 



Distributed in the north eastern Atlantic, Bay of Biscay, off 
northwest Africa and the Azores at abyssal rise depths. 
Depth range: 1354-3301 m. 

Shell description (Figs. 95-98). Shell ovate, moderately 
inflated, smooth with very fine concentric lines near ventral 
margin forming slight ridges in larger specimens, occasionally a 
few faint radial lines are present in larger specimens; perios- 
tracum pale straw-coloured, slightly iridescent; umbos very 
slightly anterior of midline, moderately inflated; proximal dor- 
sal margin straight or slightly concave on either side of umbo, 
antero-dorsal and anterior margin merge in an even curve in 
most specimens, distally postero-dorsal margin slopes down to 
posterior margin; posterior margin with slight angulation, poste- 
rior limit of anterior and posterior margins dorsal to horizontal 
mid-plane, ventral margin a smooth curve; hinge plate relatively 
narrow, barely extending to outer margins of adductor muscles, 
anterior hinge line relatively straight, distally slopes away from 
dorsal shell margin, chevron-shaped teeth small, posterior hinge 
line slightly curved anteriorly, with same number of teeth in 
each series (8/8 in a specimen 2.2 mm and 12/12 in a specimen 
3.5 mm); ligament amphidetic, small, rounded, extends below 
hinge plate. 

Prodissoconch length: c. 190 u.m. Maximum recorded shell 
length: 3.65 mm. 

There is a slight increase in the post-umbonal length as 
length increases, otherwise the ratios of height/length and 
width/length remain constant. 

Internal morphology (Fig. 99). The mantle edge is well- 
developed, particularly the inner muscular fold which at its 
dorsal edge, contains secretory cells beneath the main rejec- 
tion tract. Postero-ventral to the siphons, both the middle 
and inner folds are increased in size, convoluted and heavily 
ciliated and form a feeding aperture. Exhalent and inhalent 
siphons are combined, the latter being open ventrally. A pair 
of lateral haemocoelic canals are present the junction 



50 
40 
80 

60 
60 
50^ 



w\ L • •>*;*$:•,. 



H\L 



•• • • •• ♦ 



PL\TL 



. % :'.%>>. 






Length (mm) 

Fig. 98 Yoldiella insculpta. Variation in the ratios of height H/L, 
width W/L and postero-umbonal length PT/TL to length against 
length of a sample from Sta. BG IV DS 62, West European 
Basin. 





Fig. 99 Yoldiella insculpta. Lateral views from the right and left 
sides of the internal morphology of a specimen from Sta. S 65, 
West European Basin. (Scale = 1.0 mm). For identification of 
parts see Fig. 34. 

between the siphons. The siphonal tentacle is large and found 
equally to either the right or left side of the siphonal 
embayment. There is a well-developed anterior sense organ. 
Adductor muscles are slightly unequal in size, the anterior 
being the larger. 

Gill plates are relatively small and difficult to count in 
preserved specimens (maximum recorded c. 18-20). The 
labial palps are well-developed with approximately up to 26 
closely spaced ridges on each inner face. The palps extend 
between 1/3-1/2 across the body and each bears a long thin 
palp proboscis. The mouth is positioned a short distance 
posterior to the anterior adductor muscle. The foot is rela-i 
tively large with a broad sole with a small papilla at the i 
posterior limit. There is a large byssal gland in the heel (Fig. '■ 
100). The arrangement of pedal retractor muscles is similar to 
that of other species of Yoldiella. The cerebral ganglia are 
relatively large, the visceral ganglia are small and elongate. 
The pedal ganglia lie ventral to the style sac in the proximali 
part of the foot and are moderately large. The stomach is 
displaced slightly to the right of the body and is of moderate 
size with a large style sac. The hind gut configuration is| 
unique. There are three loops to the right of the body and two 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



63 



loops to the left of the body with a further double loop 
passing to the left of the stomach into the foot anterior to the 
stomach. The loops do vary slightly in their extent and 
curvature. This is similar to the condition in Y. subcircularis, 
Y. biguttata and Y. ovata but with an additional loop on the 
right. The hind gut has a typhlosole along its entire length. 
Fine material similar to that present in the stomach was seen 
in the digestive diverticula of a number of specimens. The 
kidney is well-developed. Sexes are separate. 

The maximum diameter of the ovum as observed in sec- 
tions of females from samples taken in February and August 
was similar (130 (xm). There seems to be a wide variation in 
the numbers of ova present. A female collected in August 
(2.74 mm) had 255 ova while another collected in February 
(3.09 mm) had only 65 ova. Maturing gonads were recorded 
for all months sampled. 

Yoldiellajeffreysi (Hidalgo 1877) 

Type locality. H.M.S. Valorous Sta. 16, Iceland Basin, 
west of Rockall Plateau, south Maury Channel, 55°10'N, 
25°58'W, 23.8.1875, Dredge, 1785 fm. 

Type specimen. Holotype: not designated; Lectotype: U.S. 
Natl. Mus., No. 199696 as here designated. 

Leda lata Jeffreys 1876, 1876. p. 431 (in part). 

Leda jeffreysi Hidalgo 1877, p. 396; Jeffreys 1879, p. 579, pi. 

46, Fig. 2; Dall 1881, p. 124; Smith 1885, p. 234; Dautzen- 

berg 1889, p. 75; Dautzenberg & Fischer 1897, p. 204; 

Locard 1898, p. 353. 
Portlandia jeffreysi Posselt 1898, p. 36. 
Yoldiellajeffreysi Verrill & Bush 1898, p. 866, pi. 81, Fig. 5, 

pi. 83, Fig. 3. 

A holotype of Y. jeffreysi was never designated but the 



following USNM specimens were identified as syntypes by 
Waren (1980):- 

No. 1999695, Valorous Sta. 9; No. 199694, and No. 199696, 
Valorous Sta. 16; No. 199700, Porcupine Sta. 20; No. 
199701, Porcupine Sta. 16 & 17; No. 199698 Porcupine Sta. 
30. 

and in the BM(NH):- 

No. 77.11.18.25, Valorous Stas. 9, 12, 13, 16; No. 
85.11.5.592-593,Porcupine Sta. 31; No. 85.11.5 366-367, 
Porcupine Sta. 16; No. 85.11.5. 591, Porcupine Sta. 9. 

Jeffreys original specimens were taken from the North 
Atlantic (Valorous Stations 9, 12, 13 & 16 and from which he 
described his species Leda lata (Jeffreys, 1896). Unfortu- 
nately the material from these four 'Valorous' Stations, which 
we have examined, contains two species of Yoldiella which 
are, superficially, similar in form (p. ). Furthermore the 1876 
description is so general that there is nothing to indicate 
which of the two species Jeffreys chose when he described 
Leda lata. Thus, we here accept Leda jeffreysi Hidalgo (1877) 
as the first unequivocal specific designation and which Jef- 
freys (1879) himself accepted two years later. 

We have also examined specimens referred to as Yoldiella 
jeffreysi by Verrill & Bush (1898) (USNM, No. 4888) and 
these clearly differ from Y. jeffreysi s.s. in being stouter, with 
a more inflated umbo, a broader hinge plate, with teeth of 
different form and fewer in number. 

Y. jeffreysi is a very widespread species. It occurs from the 
base of the continental slope to the deepest abyssal depth. In 
our samples it occurs in the Argentine, Guyana, North 
America, West European, Canary, Cape Verde & Angola 
Basins. It has also been recorded from the Gulf of Mexico 
(2416-2868 m) and from off West Greenland (3200 m) and in 
the Mediterranean off Palermo. 

Depth range: 2040-4862 m. The depth distribution is 
similar throughout the Atlantic. 




Fig. 100 Yoldiella insculpta. Transverse section through the 
'byssal' gland. (Scale = 0.1 mm). Abbreviations see p. 12. 



Material. 














Cruise 


Sta 


DepthNo 


Lat 


Long 


Gear Date 






(m) 












NORTH AMERICA BASIN 










Atlantis II 


64 


2886 


7 


38°46.0'N 


70°06.0'W 


ET 


21. 8.64 


12 


72 


2864 


6 


38°16.0'N 


71°47.0'W 


ET 


24. 8.64 


Chain 50 


76 


2862 


32 


39°38.3'N 


67°57.8'W 


ET 


29. 6.65 




77 


3806 


109 


38°00.7'N 


69°16.0'W 


ET 


30. 6.65 




78 


3828 


57 


38°00.8'N 


69°18.7'W 


ET 


30. 6.65 




84 


4749 


16 


36°24.4'N 


67°56.0'W 


ET 


4. 7.65 




85 


3834 


413 


37°59.2'N 


69°26.2'W 


ET 


5. 7.65 


Atlantis II 


123 


4853 


4 


37°29.0'N 


64°14.0'W 


ET 


22. 8.66 


24 


124 


4862 


1 


37°26.0'N 
- 37°25.0'N 


59°59.5'W 
63°58.0'W 


ET 


22. 8.66 




126 


3806 


138 


39°37.0'N 
- 39°37.5'N 


66°47.0'W 
66°44.0'W 


ET 


24. 8.66 


Atlantis II 


175 


4667- 


53 


36°36.0'N 


68°29.0'W 


ES 


29.11.67 


40 




4693 






68°31.0"W 






Chain 106 


330 


4632 


155 


50°43.5'N 
- 50°43.3'N 


17°51.7"W 
17°52.9'W 


ES 


24. 8.72 




334 


4400 


49 


40°42.6'N 
_ 40°44.0'N 


46°13.8'W 
46°14.6'W 


ES 


30. 8.72 




335 


3882- 
3919 


28 


40°25.3'N 


46°30.0'W 


ES 


31. 8.72 


Knorr 35 


340 


32164- 13 


38°14.4'N 


70°20.3'W 


ES 


24.11.73 



64 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



GUYANA BASIN 



Knorr 25 



287 



288 



291 



306 



307 



3356 

4980- 

4934 

4417- 

4429 

3859- 

3868 

3392- 

3429 

3862- 

3835 



38°17.6'N 70°22.8'W 



31 



155 



38 



30 



1316.0'N 

- 13°15.8'N 
11°02.2'N 

- 11°03.8'N 
10°06.1'N 

- 10°06.6'N 

9°31.1'N 

12°34.4'N 

- 12°40.8'N 



54°52.2'W 
54°53.1'W 
55°05.5'W 
55°04.8'W 
55°14.0'W 
55°15.4'W 
56°20.6'W 

58°59.3'W 
59°09.2'W 



ES 24. 2.72 



ES 25. 2.72 



ES 26. 2.72 



ES 2. 3.72 



ES 3. 3.72 



ARGENTINE BASIN 
Atlantis II 259 3305- 
60 3317 



30 37°13.3'S 52°45.0'W ES 26. 3.71 



WEST EUROPEAN BASIN 
Chain 106 316 2173- 85 
2209 
318 2506 106 



Jean Charcot 
(Polygas) 
(Biogas II) 
(BiogasIII) 

(Biogas IV) 



(Biogas V) 
(Biogas VI) 



(Incal) 



321 

323 

DS23 
DS25 
DS31 
DS37 
DS71 
DS51 
DS52 
DS53 
DS54 
DS58 
DS62 
DS63 
DS64 
CV38 
DS68 
DS71 
DS74 
DS78 
DS79 
CP10 
DS01 



2290- 94 
2968 

3356- 6 
3338 

4734 1 
2096 2v 
2813 11 



2110 
3546 



2430 27 



2006 
4425 
4659 
2775 
2175 
2126 
2156 
2695 
4550 
2194 



1 

1 

1 

10 

1 
1 
2 
2 
1 
2 



2777 2+2v 

4706 1 

4715 2 

2878 1 

2091 73 



DS02 2081 67 

CP01 2068- 10 

2040 
CP02 2091 2 

CP03 2466 4 

CP04 2483- 2 

2513 
DS05 2503 123 

DS06 1494 243 

DS07 2884 267 

DS08 2891 32 

CP05 2884 58 

CP06 2888- 39 

2893 
CP07 2896 17 

DS09 2897 274 



50°58.7'N 
50°57.7'N 
50°27.3'N 
50°26.8'N 
50°12.3'N 

50°08.3'N 

46°32.8'N 
44°08.2'N 
47°32.5'N 
47°31.8'N 
47°28.3'N 
44°11.3'N 
44°06.3'N 
44°30.4'N 
46°31.3'N 
47°34.1'N 
47°32.8'N 
47°32.8'N 
47°29.2'N 
47°30.9'N 
46°26.7'N 
47°34.4'N 
47°33.0'N 
46°31.1'N 
46°30.4'N 
47°29.6'N 
57°59.7'N 
57°59.2'N 
57°58.8'N 
57°58.5'N 
57°57.7'N 
57°56.4'N 
57°58.4'N 
57°57.7'N 
56°33.2'N 
56°32.5'N 
56°33.2'N 
56°31.5'N 
56°28.1'N 
56°27.6'N 
56°26.6'N 
56°25.9'N 
55°00.7'N 
55°01.0'N 
55°02.0'N 
55°01.9'N 
55°00.4'N 
55°00.9'N 
55°02.3'N 
55°02.6'N 
55°03.4'N 
55°04.4'N 
55°07.7'N 
55°08.1'N 



13°01.6'W 
13°01.3'W 
13°20.9'W 
13°19.9'W 
13°35.8'W 

13°53.7'W 

13°50.9'W 

10°21.0'W 

4°15.7'W 

9°04.2'W 

8°34.6'W 

9°07.2'W 

4°15.4'W 

4°22.4'W 

4°56.3'W 

10°29.1"W 

9°08.2'W 

8°40.0'W 

8°35.0'W 

8°30.7'W 

8°59.5'W 

10°23.9'W 

8°33.8'W 

9°07.8'W 

10°23.8'W 

10°27.1'W 

9°04.5'W 

10°39.8'W 

10°41.3'W 

10°48.5'W 

10°49.2'W 

10°55.0'W 

10°42.8'W 
10°44.6'W 
11°11.3'W 
11°12.4'W 
11°11.3'W 
11°12.4"W 
11°11.7'W 
11°12.0'W 
11°10.5'W 
11°10.7"W 
12°31.0'W 
12°32.0'W 
12°34.6'W 
12°33.4'W 
12°29.4'W 
12°31.1'W 
12°40.3'W 
12°41.7'W 
12°46.4'W 

12°52.6'W 
12°53.2'W 



ES 18. 8.72 

ES 19. 8.72 

ES 20. 8.72 

ES 21. 8.72 



DS 26. 

DS 1. 

DS 19. 

DS 24. 

DS 28. 

DS 18. 

DS 18. 

DS 19. 

DS 21. 

DS 23. 

DS 26. 

DS 26. 

DS 26. 

CV 24. 

DS 19. 

DS 20. 

DS 21. 

DS 25. 

DS 26. 

CP 21. 

DS 15. 



10.72 

11.72 

4.73 

8.73 

8.73 

2.74 

2.74 

1.74 

2.74 

2.74 

2.74 

2.74 

2.74 

2.74 

6.74 

10.74 

10.74 

10.74 

10.74 

10.74 

7.76 



DS 16. 7.76 

CP 16.7.76 

CP 16. 7.76 

CP 17. 7.76 

CP 17. 7.76 

DS 18. 7.76 

DS 18. 7.76 

DS 19. 7.76 

DS 19. 7.76 

CP 19. 7.76 

CP 19. 7.76 

CP 20. 7.76 

DS 20. 7.76 



CP08 2644 


49 


50°14.7'N 
■ 5015. 2'N 


13°13.5'W 
13°14.8'W 


CP 


27. 


7.76 


DS10 2719 


48 


50°12.7'N 
■ 50°13.2'N 


13°16.6'W 
13°16.4'W 


DS 


27. 


7.76 


OS01 2634 


794+ 
52v - 


50°14.4'N 
■ 50°15.2'N 


13°10.9'W 
13°11.0'W 


OS 


30. 


7.76 


WS01 2550- 39+2v 50°19.4'N 


13°08.1'W 


WS 


30. 


7.76 


2539 




■ 50°19.3'N 


13°06.0'W 








WS02 2498- 416 


50°19.3'N 


12°55.8'W 


ws 


30. 


7.76 


2505 




■ 50°20.0'N 


12°56.0'W 








CP10 4823 


1 


48°25.5'N 
■ 48°26.3'N 


15°10.7'W 
15°09.8'W 


CP 


31. 


7.76 


DS11 4823 


1 


48°18.8'N 
■ 48°13.6'N 


15°11.5'W 
15°12.0'W 


DS 


1. 


8.76 


WS03 4829 


5+lv 


48°19.2'N 


15°23.3'W 


WS 


1. 


8.76 


CPU 4823 


2 


48°20.4'N 
■ 48°21.1'W 


15°14.6'W 
15°13.7'W 


CP 


1. 


8.76 


OS02 4829 


4 


48°19.2'N 


15°15.7'W 


OS 


2. 


8.76 


DS14 4254- 


1 


47°32.8'N 


9°35.4'W 


DS 


7. 


8.76 


4248 














DS16 4268 


1 


47°29.8'N 
• 47°30.3'N 


9°33.4"W 
9°33.4"W 


DS 


9. 


8.76 


CANARY BASIN 














Discovery 6704 2129 


17 


27°44.9'N 


14°25.0'W 


ED 


17. 


3.68 


CAPE VERDE BASIN 














Discovery 8521 3053- 


90 


20°46.9'N 


18°43.4'W 


WS 


25. 


6.74 


3058 




■ 20°47.6'N 


18°53.5'W 








8521 3064- 


52 


20°47.9'N 


18°53.4'W 


WS 


26. 


6.74 


307 




■ 20°48.6'N 


18°53.4"W 








8532 3112- 


36 


13°47.8'N 


18°14.0'W 


WS 


5. 


7.74 


3119 




13°48.0'N 


18°14.8'W 








8532 2952- 


20 


13°48.2'N 


18°08.0'W 


WS 


5. 


7.74 


2958 




13°47.6'N 


18°07.5'W 









ANGOLA BASIN 
Atlantis II 197 4592- 
42 4597 

CAPE BASIN 

Jean Charcot DS06 4585 

(Walvis) 



35 10°29.0'S 9°04.6'E ES 21. 5.68 



33°34.5'N 2°32.9'E DS 31.12.78 



Shell description (Figs. 101-103). Shell ovate, somewhat 
inflated, inequilateral, fragile, frequently with broad, 
opaque, concentric banding which is variable in form; umbo 
inflated, anterior in position, orientated medially; dorsal shell 
margins slope gently from umbo, antero-dorsal, anterior and 
antero-ventral margins form a smooth curve, anterior limit of 
which lies dorsal to the mid horizontal line, ventral margin 
smoothly curved, with posterior limit of shell also dorsal to 
mid horizontal line, postero-dorsal margin slightly convex, 
slope increases moderately sharply at posterior limit of hinge 
plate to join posterior margin to form slight subrostration; 
hinge plate, stout, with relatively large chevron-shaped teeth, 
posterior series with one or two more teeth than anterior 
series (maximum 10 in posterior series), teeth extend as far as 
the anterior and posterior margins of anterior and posterior 
adductor muscles respectively, hinge plate lies close to shell 
margin below umbo; ligament moderately sized, amphidetic, 
'saddle'-shaped in lateral view, extends below hinge plate. 

Prodissoconch length: 187-198 jxm. Maximum recorded 
shell length: 3.7 mm. 

The species has a high degree of variation in shape and 
within a population may range from the form described above 
(the most common) to a more quadrangular outline in which 
the deepest part of the ventral margin instead of being 
approximately central is posterior to vertical line through the 
beaks (Fig. 104). Such specimens may be more inflated. 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 

Table 2 Yoldiella jeffreysi; ratios of Posterior Length (PL), Height (H), Width (W), to Total Length (TL) and other parameters. 



65 



Basin 



Max. recorded 


PL/TL 


H/TL 


W/TL 


ProdissoconchN 


length (mm) 


(mean) 


(mean) 


(mean) 


length ((Jim) 


3.70 


48/60 


69/75 


33/53 


187-198 (54) 




(54) 


(72) 


(45) 




3.49 


52/58 


68/75 


32/48 


185-198(17) 




(56) 


(70) 


(41) 




2.84 


51/56 


70/76 


38/46 


190-200 (52) 




(54) 


(72) 


(42) 




2.54 


47/55 


69/77 


35/52 


182-189 (38) 




(51) 


(73) 


(40) 




2.96 


48/58 


69/76 


34/43 


200-210 (35) 




(54) 


(73) 


(40) 




2.95 


44/60 


69/75 


36/49 


182 (25) 




(53) 


(72) 


(41) 





W. European 
Incal DS07 
Canary 
Sta. 6704 
Cape Verde 
852 1 6 

N. America 
Sta. 126 
Guyana 
Sta. 291 
Argentine 
Sta. 259 




Fig. 101 Yoldiella jeffreysi. Lateral view of a shell from the left 
side and an inner view of a right valve to show detail of the 
hinge-plate. Specimens from Sta. 316, West European Basin. 
(Scale =1.0 mm). 

The populations in different basins also differ somewhat in 
overall shape (Fig. 105). In the Atlantic, more southerly 
populations are somewhat less inflated and large specimens 
have an extended posterior margin and thus a more inequilat- 
eral shape. Overall, populations in the western Atlantic have 
a similar shape to the majority of specimens from the 
northern part of the West European Basin and they are 
inflated to a similar degree. The more southern populations 
are more extended posteriorly. Specimens from the Argen- 
tine Basin are slightly more inflated but less so than those 
from the northern West European Basin. 

It is a general feature of all populations that the width/ 
; length and post-umbonal length/total length increase with 
I increasing length. In contrast, there is little change in the 
, height/length ratio (Fig. 105). 

The inter- and intra- variability in the shape of populations 
of deep sea protobranchs has been noted in many taxa and 
most recently for the family Malletiidae (Sanders & Allen 
1985). Yoldiellid species are no exception and Y. jeffreysi is 



an extreme example (see Table 2). So much so that we have 
made a particular study of this species and we propose to 
present our results in more detail in a following publication. 

The most closely related (but distinct) species to Y. jeffreysi 
is Yoldiella lata. Jeffreys (1876) failed to distinguish between 
the two species in his samples from depths where their 
distributions overlap (Y. lata is confined to slope depths (see 
p. 32). In general Y. jeffreysi is more inflated than Y. lata, has 
more hinge teeth and the posterior adductor muscle (usually 
visible through the shell in live specimens) is smaller and 
more elongate. 

Internal morphology (Fig. 106-107). The exhalent and 
inhalent siphons are combined the latter being open ventrally 
(Fig. 106). There is a moderately well-developed feeding 
aperture immediately ventral to the inhalent siphon. A large 
siphonal tentacle, more frequently on the left side originates 
close to the base of the siphon. Antero-ventrally there is a 
well-developed mantle sense organ. The adductor muscles 
are unequal in size. The anterior is between two and three 
times larger than the posterior. The posterior is oval in shape 
while anterior is 'bean'-shaped; the 'quick' and 'catch' parts 
are clearly distinct. 

The gills are relatively well-developed with 12-19 alternat- 
ing gill plates, the number depending on the size of the 
animal. The most posterior plate lies close to the junction 
between the inhalent and exhalent siphons and to which the 
gill axes join. The labial palps are relatively small with long 
and slender palp proboscides. In their contracted state they 
extend across one quarter to one third of the body. The palps 
have been 11-14 palp ridges, again the number depending on 
the size of the animal. The foot is large and in some 
specimens it is preserved in a very long, anteriorly extended 
fashion. It has a deep papillate sole. A large byssal gland is 
present and in many specimens in the region of its aperture at 
the posterior margin of the foot there is a considerable 
amount of mucous material present. 

The species has a very large stomach, the dorsal wall of 
which lies close to the hinge plate, the stomach lies off centre 
slightly to the left. A large style sac penetrates deep into the 
foot. The gastric shield extends close to the opening of the 
oesophagus, the latter slightly to the right on the antero- 
dorsal wall. Right and left digestive diverticula are anterior 
within the body and material similar to that found in the 
stomach was observed in sections of both right and left 
diverticula. The hind gut forms a clockwise loop to the right 



66 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 





4-, 



3- 



E 
E 



o> 



4) 

.C 
(0 



2- 



1- 



i r 



1 — r 
5 



T T 



"I — r 
9 



No. of teeth 



Fig. 103 Yoldiella Jeffrey si. The relationship of the number of 
hinge-teeth to shell length of a subsample from Sta. 316, West 
European Basin. The left and right limits of each bar indicate the 
number of anterior and posterior hinge-teeth respectively. 

anterior of the body, thereafter describing an 'S'-shaped bend 
before continuing as an anticlockwise loop which partially 
overlies the first. Thereafter it runs parallel to and immedi- 



Fig. 102 Yoldiella jeffreysi. a, lateral view of a 
right and left valve of a specimen from the 
Jeffreys collection labelled Leda lata (USNM 
No. 199695, Valorous Expedition, Sta. 9). b, a 
dorsal and lateral view from the right side of a 
specimen from Sta. INCAL DS 06, West 
European Basin. (Scale = 1.0 mm). 

ately below the dorsal margin to the anus (see Fig. 107). A 
typhlosole is present along its entire length. The configura- 
tion of the hind gut on the right side of the body, despite | 
being somewhat variable is characteristic of this species (Fig. 
108). It can be very simply visualized as a doubled length of 
rope making one and a half turns (Fig. 107). In this species, 
more than any other we have examined, there is a consider- 
able variation in the course of the hind gut which can easily be 
resolved by reference to the rope analogy (Fig. 107). It would 
appear that this manner of accommodation of a long hind gut 
is particularly susceptible to distortion during development, 
possibly because of displacement due to the large size of the 
stomach and the anterior arrangement of the digestive diver- 
ticula or possibly because the loop tends to impede its own 
development in this particular configuration (Fig. 105). 

The nervous system is well-developed with moderately ' 
large 'club'-shaped cerebral ganglia, slightly smaller elongate 
visceral ganglia and large, oval, pedal ganglia. Dorsal to the 
latter are large, round, statocysts, filled with refractile gran-j 
ules. The visceral ganglia lie some distance anterior to the 
posterior adductor. 

The populations from the different basins have similar 
internal morphologies. 

Sexes are separate and the gonads overlie other internal 
organs. Gonad development was followed in two Incal 
samples (DS07, DS09; West European) and one Discovery 
sample (8521 No. 1, Cape Verde). In West European speci- 
mens the number of ova ranged from 160 (108 um maximum 
diameter) in a female 2.1 mm long to 350 (144 u.m max. 
diameter) in a female 3.1 mm long. The females from thei 
Cape Verde Basin (2.2, 2.5 & 2.7 mm total length) contained 
fewer eggs 41-103 but these had a slightly larger size range 
130-156 |xm. 

In July/August samples, maturing gonads had become 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



67 






Fig. 104 Yoldiella Jeffrey si. A comparison of selected specimens 
from a number of deep-sea Basins showing the range in shell 
shape. The shell outlines of each specimen are drawn in dorsal 
and right lateral view, a & b, Sta. 197, Angola Basin; c, Sta. 288, 
Guyana Basin; d, Sta. 334, North America Basin; e & f , Sta. 259, 
Argentine Basin; g, Sta. 316, West European Basin; h, Sta. 85, 
North America Basin. (Scale = 1.0 mm). 



Dbvious (Fig. 109) and by October the gonads had largely 
filled the body. 



Yoldiella enata (new species) 

Type locality. R.V. Knorr, Sta. 301, Guyana Basin, 
J29.1.1972, 8°12.4'N, 55°50.2'W, Epibenthic Dredge, 
'487-2500 m. 



60 



40 



80 



60 



601 



W\L 






•*ti.y 






50 



PLATL 



t.'i 



60 

40 
80 

60 
60 
50 



W\L 



. •> •. •' 



H\L 



~i '..». 



PL\TL 



■*»■:•■ ■• 



Length (mm) 



Pype specimen. Holotype: BM(NH) 1992033. Paratypes: in 
:ollection held by J. A. Allen. 

Material. 



Sta Depth No Lat Long 

(m) 



Gear Date 



pUYANA BASIN 

iinorr25 301 2487- 175 8°12.4'N 55°50.2'W ES 29. 1.72 

2500 
303 2842- 23 8°28.8'N 56°04.5'W ES 1. 3.72 

2853 



Fig. 105 Yoldiella Jeffrey si. Variation in ratios of height H/L, width 
W/L and postero-umbonal length PL/TL to length against length 
of a, samples from Sta. 126, North America Basin (large closed 
circles) and Sta. 259, Argentine Basin (points); and of b, samples 
from Sta. INCAL DS 07, West European Basin (points) and Sta. 
6704, Canary Basin (large closed circles). 



ES 18. 8.66 



Several specimens of this species are included in a mixture of 
species contained with U.S. Natl. Mus. No. 108197, labelled 
Yoldiella pygmaea Munst. None of these correspond to Leda 



NORTH At 


4ERK 


:a basin 






Atlantis II 


118 


1135- 20 


32°99.4'N 


64°34.9'W 






1153 


32°19.0'N 


64°34.8'W 



68 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 




Fig. 106 Yoldiella jeffreysi. Siphons as seen from the ventral side 
of a preserved specimen form Sta. 85, North America Basin. 
(Scale = 0.1 mm). 





Fig. 107 Yoldiella jeffreysi. Lateral views from the right and left 
sides of the internal morphology of a specimen from Sta. 85, 
North America Basin. (Scale = 1.0 mm). For identification of 
parts see Fig. 34. 




Fig. 108 Yoldiella jeffreysi. Diagrammatic views of the course of 
the hind gut as seen from the right side to show variations in the 
configuration. 

pygmaea Munst. as exemplified by U.S. Natl. Mus. No. 
197285. 

Distributed in the western Atlantic from southern limit of 
the North America Basin to Guyana, from mid to lower slope 
depths. Depth range: 1135-2853 m. 

Shell description (Figs. 110 & 111). Shell ovate, not 
particularly inflated, moderately elongate, slightly inequilat- 
eral, faint concentric striae particularly close to ventral mar- 
gin; umbo moderately large; postero-dorsal and antero- 
dorsal margins slightly convex and slope gently from umbo, 
anterior margin rounded, anterior limit dorsal to mid hori- 
zontal plane, dorsal and ventral margins without angulation, J 
antero-ventral margin smooth curve, postero-ventral margin 
very slightly sinuous posterior margin not angulated, broadly 
blunt, posterior limit in mid horizontal plane; hinge moder- 
ately broad distally, narrows centrally, chevron-shaped teeth 
robust, close set with ventral arm twice length of dorsal, 
anterior and posterior plates with up to 7 teeth; ligament 
amphidetic, moderately large, extends ventral to hinge plate. 

Prodissoconch length: - 287 u,m. Maximum recorded shell 
length: 3.65 mm. 

This species is similar to Yoldiella ella, however it is less 
round in outline, shallower dorso-ventrally and less inflated. 
The ligament is also similar to that of Y. ella as is the hinge 
plate, however, the latter in Y. ella is more broad and bears 
one or two more teeth than that in Yoldiella enata. 

Internal morphology (Fig. 112). This is similar to that of 
Yoldiella ella so much so that it is extremely difficult to 
distinguish between the two species. Such distinction as there 
is is a matter of slight difference in proportion. Thus, the 
anterior adductor muscle is slightly larger, the diameter of the 
hind gut is slight less and the exhalent siphon is somewhat 
larger than in Y. ella. Sections of the tightly coiled hindgut 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



69 




▲ 

3 



Fig. 109 Yoldiella jeffreysi . Length frequency histogram superimposed by a gonadial index. 1, immature, no gonadial development seen in 
the intact specimen; 2, first sign of gonadial development at ventral edge of visceral mass; 3, gonad surrounds the periphery of the visceral 
mass; 4, gonad covers half the visceral mass; 5, visceral mass wholly covered by gonad. Top, females; bottom, males. 

specimen a few eggs were present in the mantle cavity. This is 
not taken as evidence of brooding. 

It is clear that Yoldiella enata and Yoldiella ella are very 
closely related, however, we have no difficulty in distinguis- 
ing them from their shell features. It should also be noted that 
the depth distribution of the two species is very different, 
Yoldiella enata is found on the lower slope while Yoldiella ella 
is truly abyssal. 

Yoldiella ella (new species) 

Type locality. R.V. Chain Sta. 334, North America Basin, 
30.9.1972, 40°42.6'N, 46°13.8'W - 40°44.0'N, 46°14.6'W, 
Epibenthic Trawl, 4400 m. 

Type specimen. Holotype: BM(NH) 1992034. Paratypes in 
collection held by J. A. Allen. 




? ig. 110 Yoldiella enata. Lateral view of a shell from the right side 
and detail of the hinge-plate of a left valve. Specimen from Sta. 
301, Guyana Basin. (Scale = 1.0 mm). 

how the same number of coils. In a specimen 3.1 mm the 
palps, which are moderately small, have 14 internal ridges. 
The palp proboscides are large and broad. The kidney is large 
ind extends anteriorly lateral to the stomach. The largest 
pecimens are mature and in the case of one sectioned 



Material 


















Cruise 


Sta 


Depth 


No 


Lat 


Long 


Gear Date 






(m) 














NORTH AMERICA BASIN 












Atlantis II 

12 
Chain 50 


72 


2864 


1 


38°16.0'N 


71°47.0'W 


ET 


24. 


8.64 


76 


2862 


1 


39°38.3'N 


67°57.8'W 


ET 


29. 


6.65 




78 


3828 


5 


38°08.0'N 


69°18.7'W 


ET 


30. 


6.65 




85 


3834 


11 


37°59.2'N 


69°26.2'W 


ET 


5. 


7.65 


Atlantis II 


126 


3806 


4 


39°37.0'N 


66°47.0'W 


ET 


24. 


8.66 


24 








- 39°37.5'N 


66°44.0'W 








Chain 106 


334 


4400 


44 


40°42.6'N 
- 40°44.0'N 


46<T3.8"W 
46°14.6"W 


ES 


30. 


8.72 



70 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




3779 



9°49.0'S 10°33.0'E 



Fig. Ill Yoldiella enata. Outlines of shells from the right side to 
show variation in shape with growth of specimens from Sta. 301, 
Guyana Basin. (Scale = 1.0 mm). 




Fig. 112 Yoldiella enata. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 301, Guyana Basin. 
(Scale = 1.0 mm). For identification of the parts see Fig. 34. 

335 3882- 26 40°25.3'N 46°30.0'W ES 31. 8.72 
3919 

Knon-35 340 3264- 16 38°14.4'N 70°20.3'W ES 24.11.73 

3356 - 38°17.6'N 70°22.8'W 

SIERRA LEONE BASIN 

Atlantis II 148 3814- 1 10°37.0'N 18°14.0'W ES 7. 2.67 
31 3818 

149 3861 25 10°30.0'N 18°18.0'W ES 7. 2.67 

155 3730- 7 00°03.0'S 27°48.0'W ES 13. 2.67 
3783 

156 3459 4 00°46.0'S 29°28.0'W ES 14. 2.67 

- 00°46.5'S 29°24.0'W 

ANGOLA BASIN 

Atlantis II 197 3865- 2 10°29.0'S 9°04.0'E ES 21. 5.68 
42 4595 

198 4559- 4 10°24.0'S 9°09.0'E ES 21. 5.68 
4566 

199 3764- 2 9°47.0'S 10°29.0'E ES 22. 5.68 



WEST EUROPEAN BASIN 










Chain 106 


323 3356- 
3338 


9 


50°08.0'N 


13°53.7'W 
13°50.9'W 


ES 


21. 8.72 




326 3859 


12 


50°04.9'N 
- 50°05.3'N 


14°23.8'W 
14°24.8'W 


ES 


22. 8.72 




328 4426- 


9 


50°04.7'N 


15°44.8'W 


ES 


23. 8.72 




4435 














330 4632 


137 


50°43.5'N 
- c50°43.4'N 


17°51.7'W 
17°52.9'W 


ES 


24. 8.72 


Jean Charcot 












(Polygas) 


DS20 4226 


25 


47°33.0'N 


9°36.7'W 


DS 


24.10.72 




DS21 4190 


8 


47°31.5'N 


9°40.7'W 


DS 


24.10.72 




DS22 4144 


14 


47°34.1'N 


9°38.4'W 


DS 


25.10.72 




DS23 4734 


2 


46°32.8'N 


10°21.0'W 


DS 


26.10.72 


(Biogas III) 


DS41 3548 


1 


47°28.3'N 


9°07.2'W 


DS 


26. 8.73 




DS42 4104 


1 


47°32.1'N 


9°35.6'W 


DS 


27. 8.73 


(Biogas IV) 


DS55 4125 


80 


47°34.9'N 


9°40.9'W 


DS 


22. 2.74 




DS56 4050 


3 


47°32.7'N 


9^8.2'W 


DS 


23. 2.74 




DS60 3742 


6 


47°26.8'N 


9°07.2"W 


DS 


24. 2.74 


Cyros 














(Biogas V) 


DS66 3480 


21 


47°28.2'N 


9°00.0"W 


DS 


16. 6.74 




DS67 4150 


4 


47°31.0'N 


9°35.0'W 


DS 


17. 6.74 




DS68 4550 


3 


46°26.7'N 


10°23.9'W 


DS 


19. 6.74 


Jean Charcot 












(Biogas VI) 


DS75 3150 


4 


47°28.1'N 


9°07.8"W 


DS 


22.10.74 




DS76 4228 


243 


47°34.8'N 


9°33.3"W 


DS 


23.10.74 




DS77 4240 


55 


47°31.8'N 


9°34.6'W 


DS 


24.10.74 




DS78 4706 


3 


46°31.2'N 


10°23.8'W 


DS 


25.10.74 




DS79 4715 


9 


46°30.4'N 


10°27.1'W 


DS 


26.10.74 




DS80 4720 


3 


46°29.5'N 


10°29.5'W 


DS 


27.10.74 




CP13 4134 


2 


47°34.4'N 


9°38.0'W 


DS 


23.10.74 


Jean Charcot 0S02 4829 


8 


48°19.2'N 


15°15.7'W 


OS 


2. 8.76 


(Incal) 


0S05 4248- 


9 


47°31.3'N 


9°34.6'W 


OS 


7. 8.76 




4296 




- 47°32.2'N 


9°34.7'W 








0S66 4316- 


43 


46°27.3'N 


9°36.2'W 


OS 


9. 8.76 




4307 




- 47°27.9'W 


9°36.0'W 








0S07 4249 


63 


47°31.8'N 


9°34.3'W 


OS 


10. 8.76 




0S08 4327 


42 


47°29.8'N 
- 47°29.5'N 


9°39.2'W 
9°38.8'W 


OS 


11. 8.76 




WS03 4829 


7+2v 


48°19.2'N 
- 4819. l'N 


15°23.3'W 
15°22.5'W 


WS 


1. 8.76 




WS07 4281- 


30 


47°30.6'N 


9°37.1'W 


WS 


7. 8.76 




4274 




- 47°31.2'N 


9°35.7'W 








WS08 4287- 


36 


47°30.5'N 


9°33.7'W 


WS 


9. 8.76 




4301 




- 47°29.3'N 


9°34.1'W 








WS09 4277 


11 


47°28.8'N 
- 47°27.9'N 


9°34.0'W 


WS 


10. 8.76 




WS10 4354 


37 


47°27.3'N 
- 47°28.3'N 


9°39.9'W 


WS 


14. 8.76 




DS11 4823 


3 


48°19.2'N 


15°23.3'W 

15 22.5'W 


DS 


1. 8.76 




DS14 4248- 


20 


47°32.6'N 


9°35.7'N 


DS 


7. 8.76 




4254 




- 47°32.9'N 


9°35.1'W 








DS15 4211 


3 


47°33.6'N 


9°39.1"W 
9°38.5'W 


DS 


8. 8.76 




DS16 4268 


57 


47°29.8'N 
- 47°20.2'N 


9°33.4'W 


DS 


9. 8.76 




CPU 4823 


1 


48°20.4'N 
• 48°21.1'N 


15°14.6'W 
15°13.7"W 


CP 


1. 8.76 



Widely distributed throughout much of the Atlantic in North 
America, West European, Sierra Leone and Angola Basins 
at abyssal depths. With only two exceptions, all records are 

greater than 3200 m. Depth range: 2862-4829 m. 

Shell description (Figs. 113-116). Shell ovate, moderately 
inflated, inequilateral, shell with very fine concentric lines, 
ventral lines usually more conspicuous, few fine radial lines 
from umbo to ventral edge, periostracum light straw colour; 
umbo large, rounded, orthogyrate, anterior to midline, great- 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



71 




Fig. 113 Yoldiella ella. Lateral view of a shell from the right side 
and a left valve to show detail of the hinge-plate. Specimens from 
Sta. INCAL OS 06. (Scale = 1.0 mm). 

est shell height posterior to umbo; dorsal margin slightly 
convex, antero-dorsal anterior and ventral margins in a 
smooth continuous curve, postero-ventral margin rounded 
posteriorly, posterior margin in small specimens may have 
very slight, blunt, angulation, posterior limit slightly dorsal to 
horizontal midline, postero-dorsal margin curves gently from 
umbo to distal edge to hinge plate then slopes more acutely to 
posterior margin; hinge plate, long, characteristically angular 
below umbo, moderately broad proximally, narrow ventral to 
umbo, anterior and posterior ventral margins of hinge plate 
more or less straight, teeth strong, well-developed, equal 
number in anterior and posterior plates, up to 9 in specimen 
4.2 mm, ligament amphidetic, moderate in size, rectangular 
or slightly 'goblet'-shaped, short, wide, posterior external 
extension and long slender anterior external extension of 
fused periostracum. 

Prodissoconch length: 166 u.m. Maximum recorded shell 
length: 4.2 mm. 

There is little change in the width/length or height/length 
ratios with increasing size, however, posterior umbonal 
i length increases slightly and the posterior margin becomes 
more smoothly curved. 

Internal morphology (Fig. 117). The anterior sense 
organ is well-developed. Posterior mantle fusion is minimal, 
;limited to a fine bridge of tissue between the opposing inner 
mantle lobes forming a short exhalent siphon. The gill axis is 
attached laterally on either side of the bridge tissue. Ventral 
to it the inhalent siphon is reduced to a pair of unfused 
ithickened pads of tissue. The feeding aperture is poorly 
developed with a few gland cells present. Immediately ante- 
rior to the feeding aperture, the inner mantle fold is enlarged 



Fig. 114 Yoldiella ella. Outlines of shells from the right side to 
show variation in shape with growth of specimens from Sta. BG 
VI DS 76, West European Basin. (Scale = 1.0 mm). 

slightly and more obviously ciliated and may possibly indicate 
a temporary point of adhesion in the living specimen. The 
siphonal tentacle is usually to the left ventral side of the 
shallow mantle embayment. The adductor muscles are rela- 
tively small, approximately equal in size and more or less oval 
in shape. There are up to 16 gill plates and the gills are 
attached far posterior on the body wall. The gill axis is 
well-supplied with muscle fibres. The labial palps, like the 
gills, are relatively small with up to 14 ridges on their inner 
faces with the result that in preserved specimens, there is a 
marked separation of gill and palp which is unlikely to be true 
in life. The palp proboscides are relatively long and broad. 
The foot is of moderate size with a relatively wide neck and 
an elongate, deeply divided sole. There is a large byssal gland 
in the heel with a concentration of cilia around its opening. 
The heel has a terminal papilla. The cerebral and visceral 
ganglia are relatively small and 'club'-shaped in lateral view. 
The pedal ganglia is larger and slightly elongate. 

The oesophagus has a wide opening into a large stomach. 
The combined style sac and mid gut extend into the dorsal 
half of the foot. The digestive duct from the right diverticu- 
lum skirts dorsal to the hind gut loops to open into the 
anterior wall of the stomach. On the left and close to the 
oesophageal aperture is a relatively wide digestive duct from 



72 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 



60 

40 
80^ 

60 
60 
50 



W\L 



H\L 






..*."- T' l V.' "'.'••' 






PL\TL 



Length (mm) 

Fig. 115 Yoldiella ella. Variation in ratios of height H/L. width 
W/L and postero-umbonal length PL/TL to length against length 
of a sample from Sta. BG VI DS 76, West European Basin. 



from the right side (Fig. 117). The hind gut then passes to 
the mid postero-dorsal margin and thence dorsal to the 
posterior adductor muscle to the anus. There is a relatively 
shallow typhlosole along the length of the hind gut. Faecal 
rods were seen cradled by the gill axes between anus and 
the siphon. 

The kidney and heart are well-developed. The sexes are 
separate. Animals smaller than 2.15 mm total length were all 
immature with no obvious gonad present. The number of ova 
varies from 16 in an individual 2.57 mm (maximum diameter 
of ova 87 mm) to 90 in an individual 3.2 mm long (maximum 
diameter of ova 132 u.m). In samples collected in February, 
June, August and September in specimens of 2.15 mm and 
above, all have maturing ova. 

Y. ella has all the characteristics of a shallow burrowing or 
semi-submerged species i.e. a rounded, broad form, with 
short siphons in a shallow siphonal embayment. Many speci- 
mens bear hydroids attached to antero-ventral and ventral 
margins. 

Two intact specimens of a species of Yoldiella in which the 
external shell features appear to be close to Y. ella (or 
possibly Y. enata) were taken at Sta. 199 from the Angola 
Basin at a depth of 3771 metres (Fig. 118). We have hesitated 
to examine the internal anatomy of these. Unfortunately 
because of the opaqueness of the shell all that can be seen of 
the hind gut is part of one or possibly two coils to the right of 
the body, close to the anterior adductor. These specimens 
could either prove to be a new species or showing variation of 
shell form. 




Length(mm) 

Fig. 116 Yoldiella ella. Length frequency histogram of a sample 
from Sta. BG VI DS 76, West European Basin. 

the left anterior diverticulum. This latter opens mid-laterally 
into the stomach. A second duct from the posterior digestive 
diverticulum of the left side opens into the left wall of the 
stomach below the gastric tooth. The course of the hind gut is 
first anterior and then antero-ventral to the pedal ganglia 
before turning back on itself to pass dorsally posterior to 
the stomach. Thereafter it forms a series of complicated 
coils to the right side of the body the design of which can be 
derived from a doubled strand coiled clockwise as seen 



Yoldiella fabula (new species) 

Type locality. R.V. Chain Cruise 50, Sta, 85, North 
America Basin, 5.7.1965, 37°59.2'N, 69°26.2'W, Epibenthic 
Trawl, 3834 m. 

Type specimen. Holotype: BM (NH) 1992037. Paratypes: in 
collection held by J. A. Allen. 

Leda sericea Jeffreys 1879, p. 579 (in part). Two specimens 
were found in the Jeffreys collection (U.S. Natl. Mus. No. 
199590 (Fig. 119a) and No. 199589 (Fig. 119b)). Although 
these are labelled L. sericea and must have been so 
identified by Jeffreys they clearly differ from that species. 
A specimen stored with and labelled Yoldiella expansa 
(U.S. Natl. Mus. No. 697343 (Fig. 119c)) is also this 
species. All these specimens were collected off West Ire- 
land in 2500-2670 metres. 



Material 


















Cruise 


Sta 


Depth 


No 


Lat 


Long 


Gear Date 






(m) 














NORTH AMERICA BASIN 












Atlantis II 


62 


2496 


4 


39°26.0'N 


70°33.0'W 


ET 


21. 


8.64 


12 


64 


2886 


1 


38°46.0'N 


70°06.0'W 


ET 


21. 


8.64 




70 


4680 


1 


36°23.0'N 


67°58.0'W 


ET 


23. 


8.64 1 




72 


2864 


2 


38°16.0'N 


71°47.0'W 


ET 


24. 


8.64 1 


Chain 50 


77 


3806 


1 


38°07.0'N 


69°16.0'W 


ET 


30. 


6.65 




78 


3828 


6 


38°08.0'N 


69°18.7'W 


ET 


30. 


6.65 1 




84 


4749 


4 


36°24.0'N 


67°56.0'W 


ET 


4. 


7.65 




85 


3834 


cl3 


37°59.2'N 


69°26.2'W 


ET 


5. 


7.65 j 


Atlantis II 


92 


4694 


1 


36°59.2'N 


69°26.2'W 


ET 


5. 


7.65 i 


17 
















I 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



73 




\ ME 

PP 
BG 



Fig. 117 Yoldiella ella. Details of the internal morphology, a & b, whole mounts from the right and left sides respectively; c, ventral view of 
contracted siphon; d, ventral view of the sole of the foot and hindgut; e, course of the hindgut as seen from the right side. (Scales = 1.0 
mm). 

37°24.0'N 65°54.0'W ET 23. 8.66 

37°16.0'N 65°50.0'W 

38°14.4'N 70°20.3'W ES 24.11.73 

- 38°17.6'N 70°22.8'W 

38°16.9'S 51°56.1'W ES 13. 3.71 

37°36.9'S 52°23.6'W ES 14. 3.71 

43°33.0'S 48°58.1'W ES 17. 3.71 

37°40.9'S 52°10.3'W ES 24. 3.71 



50°08.0'N 13°53.7'W ES 21. 8.72 

50°08.3'N 13°50.9'W 

50°43.5'N 17°51.7"W ES 24. 8.72 

50°43.4'N 17°52.9'W 

47°31.5'N 9°40.7'W DS 24.10.72 

46°32.8'N 10°21.0'W DS 26.10.72 



Atlantis II 


125 


4825 


1 


24 








Knorr 35 


340 


3264- 
3356 


1 


ARGENTINE BASIN 




Atlantis II 


242 


4382- 


8 


60 




4402 






243 


3815- 
3822 


10 




247 


5208- 
5223 


16 




256 


3906- 
3917 


3 


WEST EUROPEAN BASIN 


Chainl06 


323 


33536- 
3338 


2 




330 


4632 


1 



Jean Charcot DS21 4190 1 
(Polygas) DS23 4734 2 





DS28 4413 


1 


44°23.8'N 


4°47.5'W 


DS 


2.11.72 




CV13 4252 


1 


47°31.8'N 


9°34.2"W 


CV 


25.10.72 




DS30 4160 


1 


47°38.3'N 


9°33.9"W 


DS 


18. 4.73 


(Biogas II) 














(Biogas III) 


DS41 3548 


1 


47°18.3'N 


9°07.2'W 


DS 


26. 8.73 




DS50 2124 


1 


44°08.9'N 


4°15.9'W 


DS 


1. 9.73 


(Biogas IV) 


DS55 4125 


3 


47°34.9'N 


9°40.9'W 


DS 


22. 2.74 




DS56 4050 


1 


47°32.7'N 


9°28.2'W 


DS 


23. 2.74 




DS57 2906 


2 


47°31.7'N 


9°06.2'W 


DS 


24. 2.74 


(Biogas V) 


DS66 3480 


1 


47°28.2'N 


9° 


DS 


16. 6.74 




DS67 4150 


2v 


47°32.0'N 


9°35.0'W 


DS 


17. 6.74 


(Biogas VI) 


DS76 4228 


1 


47°34.8'N 


9°33.3'W 


DS 


23.10.74 




DS84 4466 


1 


44°25.4'N 


4°52.8'W 


DS 


29.10.74 


(Incal) 


WS07 4281 


1 


47°30.6'N 
- 37°31.2'N 


9°37. l'W 
9°35.7"W 


ws 


7. 8.76 




WS08 4287 


2 


47°30.5'N 
- 47°29.3'N 


9°33.7'W 
9°34.1'W 


ws 


9. 8.76 




QS06 4316 


2 


46°27.3'N 
- 47°27.9'N 


9°36.2'W 
9°36.0'W 


OS 


9. 8.76 




QS07 4249 


2 


47°31.3'N 
- 47°31.3'N 


9°34.3'W 

9°34.3'W 


OS 


19. 8.76 



74 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 





DS05 2503 


1 


56°28.1'N 


iril.7'W 


DS 


18. 


7.76 










- 56°27.6'N 


11°12.0'W 










DS09 2897 


7 


55°07.0'N 


12°52.6'W 


DS 


20. 


7.76 










- 55°08.1'N 


12°53.2'W 










DS14 4254- 


1 


47°32.6'N 


9°35.7'W 


DS 


8. 


8.76 






4548 




- 47°32.9'N 


9°35.5'W 










DS16 4268 


2 


47°29.8'N 


9°33.4'W 


DS 


9. 


8.76 










- 47°30.3'N 


9°33.4'W 








GUINEA BASIN 


















DS20 2514 


2 


2°32.0'S 


8°18.1'W 


DS 






SIERRA LEONE BASIN 














Atlantis II 


149 


3861 


1 


10°30.0'N 


18°18.0'W 


ES 


7. 


2.67 


31 


















ANGOLA BASIN 
















Atlantis II 


195 


3707 


7 


14°49.0'N 


9°56.0'W 


ES 


19. 


5.68 


42 








- 14°40.0'N 


9°54.0'W 










196 


4612- 
4630 


2 


10°29.0'N 
- 10°29.5'W 


9°03.0'W 
9°04.0'W 


ES 


21. 


5.68 




197 


3865- 
4595 


5 


10°29.0'N 
- 10°29.0'N 


9°04.0'W 
9°04.0'N 


ES 


21. 


5.68 




198 


4559- 
4566 


10 


10°24.0'N 
- 9°47.0'N 


9°09.0'W 
10°29.0'W 


ES 


21. 


5.68 




199 


3764- 
3779 


2 


9°49.0'N 
- 9°41.0'N 


10°33.0'W 
10°55.0'W 


ES 


22. 


5.68 


GUYANA BASIN 
















Knorr 25 


291 


3859- 
3868 


1 


10°06.1'N 


55°14.0'W 


ES 


26. 


2.72 




303 


2842- 
2853 


2 


8°28.8'N 


56°04.0'W 


ES 


1. 


3.72 



Y. fabula is wide-spread at abyssal depths throughout the 
Atlantic in small but persistent numbers in most of the 
Atlantic Basins. Low population density and low sampling 
density probably explains the lack of records in the Guyana & 
Canaries Basins. Depth range: 2503-5223 m. 

Shell description (Figs. 119-121). Shell small, moderately 
swollen, 'bean'-shaped, inequilateral, post umbonal length 




Fig. 118 Yoldiella sp. Lateral views of two shells taken from Sta. 
119, Angola Basin. (Scale = 1.0 mm). 

40-46% of total length, sculpture regular with conspicuous 
ridges, periostracum straw coloured, often discoloured and 
brown at valve margins; umbo relatively large, posterior in 
position and inflated, directed posteriorly; proximal dorsal 
margins slightly convex either side of umbo, proximally 
evenly curved to rounded anterior and posterior margins, 
ventral margin long, smooth curve; hinge plate moderately 




Fig. 119 Yoldiella fabula. 
Lateral views of two shells 
from the right and left sides 
respectively and a left valve 
to show details of the 
hinge-plate, a, Jeffreys 
collection USNM No. 199590 
labelled Leda sericea Jeffr. 
St. 21, 1476 fm. N.W. 
Ireland, Pore. Ex. 1870; b, 
USNM No. 199589 labelled 
Leda sericea Jeff . St. 19a, 
1366 fm, W. of Ireland, Pore. 
Ex. 1869; c, USNM No. 
697343 labelled Yoldiella 
expansa Jeffreys 49°37'N, 
13°34'W. S.W. of Ireland. 
(Scale = 1.0 mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



75 



strong, extends almost to outer limit of both adductor 
muscles, anterior hinge plate with 1-2 more teeth than 
posterior, total number of teeth up to 17 depending on size, 
distal teeth small and difficult to identify; ligament internal, 
slightly opisthodetic, 'goblet'-shaped with posterior extension 
ventral to hinge plate. 

Prodissoconch length: 229 u,m. Maximum recorded shell 
length: 3.1 mm. 

The shell outline in this species is somewhat variable (Figs. 
120 & 121). It is the only yoldiellid species indeed species in 
our collections, with this highly characteristic 'bean'-shape. 
For a time we misidentified Yoldiella fabula as Y. dissimilis 
Verrill & Bush 1898. On closer examination we note that Y. 
dissimilis unlike Y. fabula is nearly equilateral, that the 
anterior hinge is oblique that the number of hinge teeth is 
greater and that an oblong prominent tooth-like process at 
the proximal end of the posterior hinge series is not present. 
Y. fabula, as all other yoldiellids, has only very small external 
anterior and posterior componants visible which are derived 
from secondary fused periostracum. 

The range in length of the specimens in the collection 
varies from 1.72 mm to 3.08 mm. The following are the 
overall proportions:- H/L ratio 0.63-0.72; W/L ratio 
0.41-0.50; and PL/TL ratio 0.40-0.46. Although these ratios 
vary the overall range is related to growth and to some 
variation in the populations. 



Internal morphology (Figs. 122 & 123). Ventral to the 
anterior adductor muscle the middle lobe of the mantle is 
modified to form a well-developed anterior sense organ. The 
combined siphon has a single lumen which is open ventrally. 
The gill axes join laterally indicating an inhalent as well as an 
exhalent component. A small, single, tentacle is present close 
to the postero-ventral margin of siphonal embayment. 
Numerous groups of glandular epithelial mantle cells are 
found peripheral to the inner siphonal aperture and the 
feeding aperture and anterior to the latter. The adductor 
muscles are large and approximately equal in size. The 
posterior adductor is oval in cross section while the anterior is 
'crescent'-shaped with 'catch' and 'quick' portions clearly 
marked. 

The gills are parallel to the dorsal posterior shell margin 
with up to 17 well-developed plates. The distal gill filaments 
lie close to the siphon. Moderately large labial palps extend 
approximately halfway across the body and have up to 20 
ridges on their inner surface. The foot is well-developed with 
a narrow neck and a deeply divided sole. At the heel there is 
a conspicuous median papilla directly posterior to the open- 
ing of the byssal gland. The byssal gland is well-developed. 
The pedal musculature is similar to Y. lata. Both cerebral and 
visceral ganglia are cylindrical and moderately well- 
developed with a stout connecting commissure. The pedal 
ganglia are circular and not particularly large. 

The oesophagus, stomach, and style sac are basically 
similar to those of Y. lata. A long duct from the right 
digestive diverticula passes dorsally over the hind gut to enter 
the stomach close to the oesophageal aperture. The duct from 
one left diverticulum opens slightly more posteriorly on left 
ventral wall, while the duct from the second left diverticulum 
opens ventral to the gastric tooth on the left side. The hind 
gut has a typhlosole and forms a single loop to the right side 
of the body. 

Initially the gonads develop ventral to the digestive diver- 



ticula and the hind gut loop, but gradully they spread 
posteriorly and dorsally to the stomach. A female 2.5 mm 
long, from a July sample had approximately 74 large ova 
(maximum diameter 180 u-m) while a second female of similar 
size (2.3 mm) had 62 ova (maximum diameter 160 urn). The 
gonadial aperture is close to that of the kidney, and anterior 
to the posterior pedal retractor muscle. The large kidney 
extends from the postero-dorsal margin to the foot and 
anteriorly over the viscera to a point just anterior to the 
lateral pedal retractor muscle. A large pericardial cavity is 
present. 

Yoldiella veletta (new species) 

Type locality. R.V. Jean Charcot, Biogas VI, Sta. DS87, 
Bay of Biscay, 31.10.1974, 44°05.2'N, 4°15.7'W, Epibenthic 
Trawl, 1913 m. 

Type specimen. Holotype: Museum National d'Histoire 
Naturelle, Paris. 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



canaries basin 

Discovery 6701 1934 1 27°45.2'N 14°13.0'W ES 16. 3.68 

CAPE VERDE BASIN 

145 2185 1 10°36.0'N 17°49.0'W ES 6. 2.67 

WEST EUROPEAN BASIN 

Jean Charcot 

Biogas VI DS87 1913 1 44°05.2'N 4°15.7'W ES 31.10.74 

Distributed on the lower slope in the eastern Atlantic from 
the Bay of Biscay to the Cape Verde Islands. Depth range: 
1913-2105 m. 

Shell description (Fig. 124). Shell moderately swollen, 




Fig. 120 Yoldiella fabula. Lateral view of a shell from the right 
side and detail of the hinge-plate of a left valve. Specimens from 
Sta. BG VI DS 84, West European Basin. (Scale = 1.0 mm). 



76 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 



60-, 

-W\l 
40 



80n 



-H\L 



-" \ ' 



60 J 

50 

40H 



PL\TL 



• . ••• 



• .••. 



1 



Length (mm) 



Fig. 121 Yoldiellafabula. Variation in ratios of height H/L. width 
W/L and postero-umbonal length PL/TL to length against length 
of specimens taken by the Biogas Expeditions as listed in the 
table of material. 



ovate, inequilateral, sculpture, fine concentric lines and 
growth rings, no lunule, no escutcheon; umbo large, poste- 
rior to midline, directed to posterior; antero-dorsal margin 
merges with anterior margin in smooth curve, limit of ante- 
rior margin close to midline, ventral margin long, shallow 
curve, limit of posterior margin ventral to midline, proximal 
postero-dorsal margin slopes more steeply than antero-dorsal 
margin and results in narrowing of post umbonal shell in 
lateral view; hinge plate moderately strong, except ventral to 
umbo where it is very narrow, hinge teeth strong, somewhat 
elongate, 1 or 2 more teeth in anterior series; ligament 
amphidetic, largely ventral to hinge margin; no chondro- 
phore. 

Prodissoconch length: 165 u,m. Maximum recorded shell 
length: 4.56 mm. 

Internal morphology (Fig. 125). The combined siphon 
has a single lumen which is open ventrally, as in Y. fabula. 
The siphonal embayment is deep, a fine tentacle is present on 
the right side. The adductor muscles are particularly large but 
approximately equal in size, the anterior being fractionally 
the larger. The anterior sense organ is not particularly 
well-developed. The gill is elongate and attenuated with up to 
27 plates. The palps are large each with up to 13 internal 
ridges. The foot is also large and with papillate margins 
anteriorly directed. The stomach is moderately large and the 
hind gut forms a single loop to the right side of the body. The 
hind gut has a wide diameter and a single typhlosole is 
present along its entire length. 

This species has clear affinities with species of Portlandia. 
Nevertheless, it is a fragile shell without any trace of lunule or 
escutcheon. On the basis of only three specimens, the shell 
morphology seems most similar to Y. fabula. 




Fig. 122 Yoldiellafabula. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 85, North America 
Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34. 




Fig. 123 Yoldiellafabula. External views of intact stomach an style 
sac in a, left; b, right and c, antero-frontal views. Dissected from 
a specimen from Sta. 85, North America Basin. (Scale = 1.0 
mm). 

Genus Portlandia Morch 1857 

Type. By selection (Soot-Ryen, 1984: Opinion 769 ICZN) 
Nucula artica J.E. Grey, 1824. 

Shell moderately small, slightly inflated, moderately frag- 
ile, oblong, posteriorly angular, more or less truncate, sub- 
rostrate, not gaping, escutcheon present, usually defined by 
weak or occasionally moderate carina, lunule may be present; 
usually glossy, smooth, postero-ventral margin may be sinu- 
ous, proximal postero-dorsal margin almost straight or 
slightly concave; umbo prominent, anterior, chondrophore 
variously developed; ligament amphidetic, largely internal 
with small part external, hind gut single loop to right of body. 

Portlandia lenticula (Moller 1842) 

Type locality. Greenland. 

Type specimen. Lectotype BM(NH) 1843.7.3.31, right-hand! 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



77 




Fig. 124 Yoldiella veletta. Lateral views of two shells from the right 
side, detail of the hinge-plate of a right valve and a dorsal view of 
a shell. Specimens form a, Sta. 145, Cape Verde Basin; b & c, 
Sta. BG VI DS 87, West European Basin; d, Sta. 6701, Canaries 
Basin. (Scales = 1.0 mm). 





Fig. 126 Portlandia lenticula. Lateral view of a shell from the right 
side from Sta. S44, West European Basin. An interval view of a 
right valve with an enlarged detail of the hinge-plate and a dorsal 
view of a shell. Specimens from North East Atlantic (det. K. 
Ockelmann). (Scales = 1.0 mm). 




Fig. 127 Portlandia lenticula. Lateral view from the right side of 
the internal morphology of a specimen from Sta. S44, West 
European Basin. (Scale = 1.0 mm) for identification of the parts 
see Fig. 34. 



Fig. 125 Yoldiella veletta. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 145, Cape Verde 
Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34. 



specimen of 5 mounted specimens; Paralectotypes BM(NH) 
1843.7.3.27-30 4 mounted specimens. 

\Nucula lenticula Moller 1842, 17. 
Portlandia lenticula Sars 1878, 39, tab. 4, Fig. 10a,b; Thiele 

1928, 617; Ockelmann 1958, Fig. 13, pi. 1, Fig. 12. 
Yoldia (Yoldiella) lenticula Richards 1962, pi. 1, Figs, 23, 24. 



Yoldiella lenticula Dautzenberg & Fischer, 1912, 406; Scar- 
lato 1981, 209. Fig. 113. 



Material. 



Cruise 



Sta 



Depth No Lat 
(m) 



Long 



Gear Date 



WEST EUROPEAN BASIN 

Sarsia 44 1739 4 43°40.8'N 

Thalassa 2438 1400 3 48°33.7'N 



3°35.2'W ED 16. 7.67 
10°15.0'W PBS 26.10.73 



78 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



Jean Charcot DS37 2110 1 47°31.8'N 8°34.6'W DS 24.8.73 

(Biogas III) 

(Biogas IV) CP01 2245 2 47°34.6'N 8°38.8'W CP 25. 2.74 

CANARY BASIN 

Discovery 6704 2129 1 27°44.9'N 14°25.0'W ED 17.3.68 

This is predominantly a northern Atlantic species occurring 
mostly from 10-200 metres (Ockelmann, 1958). Neverthe- 
less, there are sufficient past records to confirm the present 
identifications that at its southern limits it is present at lower 
slope depths. Perhaps indicative of a temperature/depth 
relationship. 

Shell description (Fig. 126). Shell moderately stout, 
ovate, slightly inequilateral, fine concentric lines, with elon- 
gate lunule and escutcheon, shell very wide dorsally and 
medially (such that when it rests on a valve the dorsal part is 
centred so that both umbos are characteristically visible in the 
lateral view); umbo very large, raised, internally directed, 
orthogyrate, immediately anterior to midline; antero-dorsal 
margin joins anterior and antero-ventral margins in a smooth 
curve, postero-dorsal margin also joins posterior and postero- 
ventral margin in smooth curve but is more attenuate than 
anterior margin; hinge plate moderately stout, not quite 
reaching level with the outer margins of adductor muscles, 
hinge plate narrows almost to margin below umbo, anterior 
and posterior hinge teeth equal in number or with one 
additional on the posterior plate; ligament amphidetic large, 
globular, extending far ventral to the hinge plate, slight 
secondary anterior and posterior external extension of fused 
periostracum. (See Ockelmann 1958, for typical shell dimen- 
sions). 



Internal morphology (Fig. 127). The combined siphons 
are short within a relatively shallow siphonal embayment. 
There is a slender sensory tentacle on the right side. The 
anterior sense organ and the feeding aperture are not particu- 
larly well-developed. The adductor muscles are very large, 
more or less oval in shape the anterior being the larger in size. 
The gills are slender with approximately 13 plates in a small 
specimen 14 mm in length. The palps are large with 13 ridges. 
The foot is small and in the one whole mount contracted to 
the level of the ventral edge of the palps. There is a small 
byssal gland. The stomach is large and the hind gut stout, the 
latter describes a single loop on the right side of the body. 

Portlandia fora (new species) 

Type locality. R.V. Sarsia, Sta. 56, Bay of Biscay, 
19.7.1967, 43°43.0'N, 3°47.8'W, Epibenthic Trawl, 641 m. 

Type specimen. Holotype: BM (NH) 1992041. Paratypes: in 
collection held by J.A. Allen. 

Material. 



Cruise Sta Depth No Lat Long Gear Date 

(m) 



WEST EUROPEAN BASIN 

Sarsia 56 641 15 43°43.0'N 3°47.8'W ED 19.7.67 

Only taken from the Bay of Biscay at one Station on the 
upper slope. Depth 641 m. 

Shell description (Fig. 128). Shell relatively stout, 




Fig. 128 Portlandia fora. Lateral 
view of a shell from the left side and 
a dorsal view of the same shell, detail 
of the hinge-plate of a left valve and 
lateral views of two small specimens 
to show variation in shape with 
growth. Specimens from Sta. S 56, 
West European Basin. (Scales = 1.0 
mm). 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



79 



inflated, ovate, inequilateral; umbos inflated, orthogyrate, 
anterior to midline; proximal dorsal margin slightly convex, 
antero-dorsal margin convex, slightly angulate at limit of 
hinge plate, then relatively straight section to dorsal limit of 
anterior margin, antero-ventral margin and ventral margin 
smoothly curved, posterior margin drawn out into broad 
rounded medial tip, postero-dorsal margin slightly convex 
sloping gradually towards tip, slight dip in outline at limit of 
hinge plate, posterior margin slightly rostrate; no marked 
rostral ridge but a small lunule and escutcheon present close 
to umbos; hinge plate moderately broad, long strong teeth, 
12 in posterior and 10 in anterior series in largest individual, 
ligament internal, amphidetic, moderately large, 'goblet'- 
shaped, short anterior and posterior external extensions of 
fused periostracal. 
Maximum observed shell length: 3.86 mm. 

Internal morphology (Fig. 129). Well-developed com- 
bined inhalent and exhalent siphons are present, the inhalent 
siphon is somewhat the shorter than exhalent. The siphonal 
tentacle is usually on the left side. The anterior sense organ is 
well-developed. The adductor muscles are relatively small. 
The anterior adductor is 'cresent'-shaped and approximately 
twice the size of the oval posterior adductor. 

The gills have up to 14 alternating filaments. The labial 
palps are small, extending over approximately 1/4 distance of 
body and have up to 9 inner palp ridges. The palp probos- 
cides are long and thin. The visceral ganglia are relatively 
slender, the cerebral ganglia are larger and more oval in 
shape and the pedal ganglia are large and round. The foot is 
moderate in size with a large byssal gland. There is a 
relatively large stomach with the style sac ventral and slightly 
posterior to it. The hind gut penetrates deep into the foot 
ventral and anterior to the pedal ganglia before turning 
dorsally to umbonal region where it passes to the right side of 
the body and forms a single loop. The hind gut has a 
typhlosole along its length. 

This species is similar in shell shape and internal morphol- 
ogy to Portlandia minuta but differs from the latter in that P. 
fora has a less angulate shell margin, slightly larger internal 




ig. 129 Portlandia fora. Lateral view from the right side of the 
internal morphology of a specimen from Sta. S 56, West 
European Basin. (Scale = 1.0 mm). For identification of parts see 
Fig. 34. 



ligament, a more obvious external ligament, is less inflated 
and has a greater number of hinge teeth, the hinge plate is 
narrower, and the post-umbonal length shorter. Anatomi- 
cally there are relatively few differences, the gill plates and 
palp ridges are marginally fewer in specimens of a similar 
size. 

Portlandia minuta (new species) 

Type location. R.V. Atlantis, II Cruise 42, Sta. 203, 
Angola Basin, 23.5.1968, 8°48'S, 12°52'E, Epibenthic Trawl, 
527-542 m. 

Type specimen. Holotype BM (NH) 1992040. Paratypes: in 
collection held by J. A. Allen. 

Material. 



Cruise 



Sta 



Depth No Lat 
(m) 



Long 



Gear Date 



CAPE BASIN 

Atlantis II 188 619-622 33 23°00.0'S 12°58.0'E ES 16.5.68 

ANGOLA BASIN 

Atlantis 42 203 527-542352 8°48.0'S 12°52.0'E ES 23.5.68 

Occurs off S.W. Africa at upper slope depths in Angola & 
Cape Basins. Depth range: 527-622 m. 

Shell description (Figs. 130 & 131). Shell small, inflated, 
subovate, posteriorly narrow, robust, fine but somewhat 
irregular concentric lines; slightly iridescent, pale yellow 
periostracum; umbos inflated, anterior to midline, internally 
directed; lunule and escutcheon barely visible; slightly ros- 
trate, slight indication of rostral ridge in some specimens; 
antero-dorsal margin convex, slopes rapidly and evenly to 
anterior margin, postero-dorsal margin slightly convex, 
slopes gradually to posterior margin, slight angle at limit of 
posterior hinge plate, ventral margin smoothly curved, cen- 
trally deep, posterior margin drawn out but moderately 
rounded, in mid horizontal plane; hinge plate strong, fairly 
narrow on either side of ligament, broadens out distally, 
distal teeth prominent, 3—4 small proximal teeth, in total 9 in 
anterior series and 11 in posterior series of largest specimen; 
ligament amphidetic, rectangular in shape, small external 
secondary extensions of fused periostracum on either side of 
umbo. 

Prodissoconch length: 166 u,m. Maximum recorded shell 
length: 2.28 mm. 

Internal morphology (Fig. 132). There is a combined 
siphon with a single lumen, thus there is no separation 
between inhalent and exhalent lumena, however, the gill axes 
join mid-laterally. Gland cells are present at the junction of 
axis and siphon. There is a well-developed elongate anterior 
sense organ. The adductor muscles are unequal in size. The 
smaller posterior muscle is oval in shape, the anterior is 
almost twice the size and 'cresent'-shaped. The gills are 
well-developed with up to 14 relatively large plates, the most 
posterior of the inner plates are clearly interlocked even in 
the preserved specimens. The labial palps are relatively small 
with up to 8 palp ridges, the most posterior of these being 
much broader than the rest. 

The foot is large but the pedal musculature is not as 
well-developed as in some Yoldiella species. There is a large 



80 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 




6CH 



W -fcfcjf 



40-1 

80 

70 



h\l- '**&*<:* 



Fig. 130 Portlandia 
minuta. Lateral views of 
shells from the left and 
right sides, detail of the 
hinge-plate of a left valve 
and the dorsal view of a 
shell. Specimens from Sta. 
203, Cape Basin. (Scale = | 
1.0 mm). 

Thereafter it makes a single loop to the right side of the body. 
A small amount of food material was observed in parts of the 
left digestive diverticulum. The kidneys are small. Gonads 
are present in specimens larger than 1.6 mm. The testes occur 
dorsally, ventrally and internally to the digestive diverticula; 
with posterior dorsal and lateral extensions. 

In the course of growth, the valves become more inflated 
and more rostrate but there is little change in the height/ 
length or posterior umbonal length/ total length ratios (Fig.| 
131). Hydroids were present on one individual and these! 
covered the dorsal and posterior shell margins. 



60- 



40 



PL\TL 






Length (mm) 



Fig. 131 Portlandia fora. Variation in ratios of height H/L, width 
W/L and postero-umbonal length PT/TL to length against length 
of a subsample taken from Sta. 203, Cape Basin. 

byssal gland in the heel with a relatively large blood space 
surrounding it. The nervous system is well-developed with 
large 'club'-shaped visceral and cerebral ganglia and large, 
round, pedal ganglia with associated large statocysts dorsal to 
them. The stomach and style sac are large. From the style sac 
the hind gut penetrates the foot for a short distance before 
turning dorsally to parallel the posterior edge of the body. 




Fig. 132 Portlandia fora. Lateral view from the right side of the 
internal morphology of a specimen from Sta. 203, Cape Basin. 
(Scale = 1.0 mm). For identification of parts see Fig. 34. 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



81 




Material 














Cruise 


Sta DepthNo 


Lat 


Long 


Geai 


Date 




(m) 












CAPE VERDE BASIN 












Discovery 


8521 6 3070- 6+2v 
3064 


20°47.9'N 


18°53.4'W 


WS 


26. 


6.74 




8528 1 3155- 72+2v 17°38.7'N 


18°35.8'W 


ws 


2. 


7.74 




3150 


17°38.3'N 


18°34.9'W 








Atlantis II 


148 31114- 1 


10°37.0'N 


18°14.0'W 


ES 


7. 


2.67 


31 


3828 














149 3861 3 


10°30.0'N 


18°18.0'W 


ES 


7. 


2.67 


ANGOLA BASIN 












Atlantis II 


195 3797 45 


14°40.0'S 


9°54.0'E 


ES 


19. 


5.68 


42 


196 4612- 1 
4630 


10°29.0'S 
10°29.0'S 


9°54.0'E 
9°04.0'E 


ES 


21. 


5.68 



Fig. 133 Portlandia abyssorum. Lateral views of three shells from 
the right side to show variation in shape. Dorsal view of a shell 
and detail of the hinge-plate of a left valve. Specimens taken from 
a, Sta. 24, Galathea Expedition, Sierra Leone Basin (Type 
specimen); b, c & d, Sta. 8528 1 , Cape Verde Basin; e, Sta. 8521 6 , 
Cape Verde Basin. (Scales = 1.0 mm). 



Portlandia abyssorum (Knudsen 1970) 

Type locality. R.V. Galathea, Sta. 24, E., Atlantic off W. 
Africa, 1950, 3°54'N, 8°22'W, Trawl, 3196 m. 

Type specimen. Holotype: Zoological Museum, University 
of Copenhagen. 

Yoldiella abyssorum Knudsen 1970, 47, Fig. 29, pi. 1, Fig. 17. 



CAPE BASIN 

Jean Charcot DS05 4560 1 33°20.5'S 

(Walvis) CP13 3550 1 32°18.1'S 



2°34.9'E DS 30.12.78 
13°15.9'E CP 12. 1.79 



Occurs at abyssal depths off the west coast of Africa, Cape 
Verde, Angola & Cape Basins. Depth range: 3064-4630 mm. 

Shell description (Figs. 133 & 134). An accurate descrip- 
tion is given by Knudsen (1970). Populations of this species 
vary somewhat in the shape of the shell outline from that of 
the type specimen to specimens with a more straight or 
slightly concave postero-dorsal margin and a more convex 
postero-ventral margin with intermediates between these two 
extremes. 

Internal morphology (Fig. 135). In contrast to the 
description of Knudsen (1970) there is an inhalent as well as 
an exhalent siphon. The short ventral inhalent siphon is not 
particularly obvious being much shorter than the exhalent, 
however, sections show a twin siphon, the inhalent being 
open ventrally. A siphonal tentacle originates on the left of 
the siphon and there is a fairly well-developed feeding 
aperture below. The adductor muscles are large, the anterior 
being approximately twice the size of the posterior. The gills 
are well-developed with up to 24 gill filaments. The labial 
palps are large with a large number of internal ridges (up to 
30), the number depending on the size of the individual. The 
foot is large and extends anterior and ventral to the anterior 
adductor muscle. It also has a large byssal gland. The cerebral 
and visceral ganglia are elongate with a moderately thick 
commissure. The pedal ganglia are large, elongate with large 
associated statocyts. The hind gut forms a single loop on the 
right side of the body and has a typhlosole along its length. 

Prodissoconch length: 187-198 \x,m. Maximum recorded 
shell length: 4.76 mm. 

This species at first sight might be confused with Yoldiella 
biscayensis, however there are a number of differences. 
These include: - the presence of a lunule and escutcheon; the 
umbo is raised only slightly above the dorsal margin; the 
posterior and postero-dorsal margin is faintly rostrate; the 
prodissoconch is much narrower and is shorter in length; the 
palps have many more ridges. 



82 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



40-W\L 
30- 
80-|H\L 
70- 



•• • 



:* * 



60- 
50- 



PL\TL 



• • • • • 



Length (mm) 



Fig. 134 Portlandia abyssorum. Variation in ratios of height H/L 
width W/L and postero-umbonal length PL/TL to length against 
length of specimens from Sta. 195, Angola Basin (closed 
triangles) and Sta. 8528', Cape Verde Basin (closed circles). 




Fig. 135 Portlandia abyssorum. Lateral view from the right side of 
the internal morphology of a specimen from Sta. 8528 \ Cape 
Verde Basin. (Scale = 1.0 mm). For identification of the parts see 
Fig. 34. 



DISCUSSION 

Of all the protobranch bivalves of the Atlantic, the yoldiellids 
are by far the most difficult nuculanid subgroup in which to 
discern evolutionary pathways. Despite the large number of 
species we believe that these are closely related within a 
subfamily. With possibly one exception, of 28 species of 
Yolidella described here, there is a fine gradation in morpho- 
logical features that both combines them within a single genus 
and distinguishes them as a separate group. It must be 



emphasized that as in all deep-sea protobranch species, the 
shell proportion changes with increasing size. In general the 
post-umbonal length increases at a rate greater than the other 
dimensions. In some cases this also applies to the height of 
the shell. As a result the small shells of a species may be 
mistaken as being of a different species. This also creates 
difficulties in making comparisons between species. 

To the experienced eye, species and subspecies can be 
separated and defined. Of particular diagnostic importance is 
the form and course taken by the hind gut. Although there 
may be some variation within a species, the course and 
diameter of the gut alone is usually diagnostic. Nevertheless, 
it is often difficult to define and only becomes clear after close 
comparison of a range of species. We can distinguish eight 
broad configurations of the hindgut of which the simplest, a 
single loop to the right of the viscera occurs in 17 of 32 species 
and subspecies of Yoldiella (Table 3) (Allen, 1992). The most 
complex configuration occurs in only one species (see below). 

The species of Portlandia form a compact group in which 
the shells are relatively robust, elongate, with the posterior 
margin approximately central to the horizontal midline. The 
hind gut has a single loop to the right and has a large 
diameter. The adductor muscles are large and oval and more 
or less equal in size. The hinge plates are long and stout, 
continuous with the amphidetic internal ligament. The lunule 
and escutcheon are usually well-defined. Three of the four 
species are from upper to mid-slope depths and one P. 
abyssorum, is from abyssal depths. The latter, apart from 
having larger palps, smaller adductor muscles and more 
dorsal anterior and posterior limits to the shell outline than 
the other species described, its morphology is basically the 
same. 

One rare species of Yoldiella, Y. veletta, has many of the 
characteristics of Portlandia described above. However, it is a 
fragile shell without lunule or escutcheon. Furthermore, the 
hinge plates form in a narrow bridge below the umbo with the 
amphidetic ligament ventral to it. With only three specimens 
at hand we defer categorical judgement, but hypothesize that 
the primitive form of Yoldiella must have had similar charac- 
teristics. 

On the premise that the simplest form of hind gut is likely 
to reflect the primitive condition we derive an evolutionary 
pattern that originates in species with this character but 
among others, for it is unwise to base evolutionary conclu- 
sions on one character alone. In passing, it should be said that 
it is a sad fact that for many malacologists, it is the shells 
rather than the viscera that are all-important. 

It seems reasonable to assume that deep-water species in 
the Atlantic originated either from shallow water, possibly 
tethyan and arctic seas, or by migration at depth from the 
Southern Ocean. For reasons that we will describe elsewhere 
(Allen and Sanders in m/s), we think it unlikely that the 
major colonization of the deep Atlantic was from high 
southern latitudes. Yet there are only a limited number of 
yoldiellids present in shelf sediments, but all of these species 
have a relatively short hindgut with a simple single loop to the 
right side of the viscera. This character is also found in other 
shallow-water nuculanids and in shallow-water neilonellids 
and tindariids, however, species of Yoldiella differ from these 
latter three groups in not having heavy, concentrically orna- 
mented shells. When concentric ornamentation is present in a 
yoldiellid it is always of a fine, delicate nature, and more 
often than not confined to the periphery of the shell. 

We identify two species from shallow water in the North 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



83 



and West Atlantic, Y. frigida and Y. robusta that have 
characters which we believe a 'stem' group might possess. 
These include, in addition to the single hind gut loop, a 
symmetrical ovate shell outine, relatively short fragile sepa- 
rate hinge plates and a moderately large central amphidetic 
ligament (Fig. 148). In addition, they have large siphons with 
combined lumena which are ventrally unfused, moderately 
large, oval, subequal, adductor muscles, a few large fringing 
papillae to the foot, a relatively elongate gill with a moderate 
number of plates and broad palp ridges which are relatively 
few in number. 

From this basic form, we derive a number of evolutionary 
pathways. The most simple derivation appears to be that 
shells become somewhat higher in proportion to length and 
the antero-dorsal and postero-dorsal margins become more 
horizontal such that the anterior and posterior limits of the 
shell are dorsal to the horizontal midline (Figs. 136-147). 
(For details of the comparative overlay technique, see Fig. 
136). In other respects, a characters are similar to those given 
above. These latter species include Y. inconspicua, Y. extensa 
and Y. argentinensis, again from the North and West Atlantic 
but further downslope than Y. frigida and Y. robusta. In 
addition, Y. curta, a common and widespread species from 
the base of the continental slope would also appear to belong 
here, however, unlike the species mentioned so far, the 
hindgut of Y. curta passes anterior to the mouth to form a 
single loop on the left side of the body. This disposition of the 
hind gut is a simple derivation from the primitive condition 
and can be explained simply in terms of elongation and 
accommodation of the hindgut. In all other respects Y. curta 
is similar to the species of the Y. frigida group. 

In juxtaposition to this possible stem group is a group of 
species centred upon Y. lucida (shelf/upper slope), Y. obesa 
(mid/lower slope) and Y. similiris (upper/mid slope). 
Although having similar ovate shape to Y. frigida and Y. 
robusta, these species have much longer but still separated 
hinge plates, smaller adductor muscles of which the posterior 
is significantly smaller than the elongate anterior muscle. The 
hind gut loops are somewhat longer and more broadly looped 
and the lumena have a wider diameter. Most other characters 
are in common with the 'stem group'. These include an 
internal amphedetic ligament ventral to the hinge plate which 
is somewhat smaller than that of the stem group, a relatively 
elongate gill, small palps with broad ridges which are few in 
number and papillae of the foot which are relatively large. 
The differences between Y. lucida, Y. obesa and Y. similiris 
and the species of the 'stem group' relate to the strength of 
the hinge plate. As the length and robustness of the hinge 
^increases there is less requirement for large adductors and a 
large ligament to ensure the integrity of the two valves. In 
addition, as the maximum depth limit of the species 
increases, the hind gut tends to enlarge either in length or 
diameter or both. 

As in the case of the 'stem group', we believe evolution 
from the 'lucida' group also involves an increase in the height 
of the shell and the antero- and postero-dorsal shell margins 
becoming more horizontal such that the posterior limit of the 
hell margin becomes characteristically sharply rounded. The 
posterior adductor muscle is reduced in size, the hind gut 
penetrates deep into the foot and the palps are small with 
j/ery few ridges. The siphonal lumena are separate. Species 
vith these characterstics include Y. bilanta, Y. hanna and Y. 
apensis, all of which are restricted to slope depths. 

Y. artipica is intermediate in its characters to the two above 



groups, however the hind gut is more sinuous in its course to 
the right. This represents the initial stage in a trend that leads 
to the coiling of the hind gut on the right side of the body. 
Note the Y. artipica has a deeper distribution than those 
species described above and is found on the abyssal rise. 
Similarly, Y. sinuosa, Y, blanda and Y. biscayensis which 
have similar characteristics to the 'bilanta'' group, all have 
sinuous hind guts. There are other internal differences shown 
by these three species. Thus, while the adductor muscles are 
dissimilar in size, the posterior muscle is not greatly reduced 
in size, the palp ridges, although wide, are more numerous 
and thus the palp is large and the siphon is particularly large 
with combined lumena. As in the case of Y. artipica these are 
species from the abyssal rise. 

The logical sequence to the trend is seen in Y. lata in which 
the hind gut has a larger diameter, has lengthened such that 
the 'reverse-S' course has progressed to a double-loop. Also 
to be noted are that the adductors are moderately large and 
are equal in size, and the hinge plates, although elongate, are 
narrow and much less robust. Similarly the gill is relatively 
small and the palp has numerous narrow ridges. 

As a continuation of this trend, a specialized group of 
species comprising Y. ella, Y. enata and Y. jeffreysi is arrived 
at. A sequence of events can be envisaged. Starting from the 
condition in Y. lucida the hind gut lengthens, remains to the 
right of the body and becomes increasingly coiled. (Up to 
four times). The shell becomes characteristically rounded, 
high with large umbos. The hinge plates become very strong 
and the ligament small and rounded. The adductor muscles 
are small, and may be subequal in size. The generating 
outline curve of the shell is rotated somewhat to the right so 
that the umbo is distinctly anterior and the maximum ventral 
limit is posterior to the vertical midline. We can envisage a 
sequence of increasing hind gut complexity from Y. lucida 
through Y. blanda, Y. lata, Y. jeffreysi to Y. enata, however, 
we have some reservations as to whether Y. ella is the 
terminal species of this line. While Y. ella has the most coiled 
hind gut of all the yoldiellids in our collections, the more 
evenly rounded shape, the extremely small subequal adduc- 
tor muscles and the massive hinge plates might indicate a 
separate derivation or at least a marked terminal divergence 
in the series. These species have a depth distribution from the 
abyssal rise to the greatest abyssal depth. There is little doubt 
in our opinion that the differences in morphology exhibited in 
both the latter group are related to the requirements of life at 
abyssal depths. 

We also derive an even more complex but distinct group 
comprising Y. americana, Y. subcircularis , Y. biguttata and V. 
ovata from the Y. lucida stock. These four species also have 
characteristically rounded, high shells which have large 
umbos. The evolutionary sequence probably included an 
intermediate stage with a form similar to that of Y. perplexa 
in which shell characters are similar but in which there is a 
relatively short single hind gut loop to the right, robust 
subequal adductor muscles, small palps and gills, large pedal 
papillae and long hinge plates. Y. americana differs relatively 
little from this, except that the hind gut is considerably 
lengthened and which takes a course to the left and right of 
the stomach and the palp is a deep semicircular shape with a 
large number of ridges (see p. 54). A similar morphology to 
that of Y. americana is found in Y. subcircularis except that 
the hindgut loops are doubled on either side of the body. 
Similarly, Y. biguttata and Y. ovata also have two hind gut 
loops to the right and the left and in Y. insculpta, the hind gut 



84 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 




e a 



r f 





Fig. 136 Yoldiella frigida (f), Y. robusta (r), & (separately) Y. 
curta(c). 



Fig. 137 Yoldiella argentinensis (a), Y. externa (e) & (separately) 
Yoldiella inconspicua inconspicua (i), Y. i. profundorum (p) & Y. 
i. africana (a). 




s I ° 
Fig. 138 Yoldiella lucida (1), Y. similirus (s) & Y. obesa incala (o). 




Fig. 139 Yoldiella bilanta (b), Y. hanna (h) & Y. capensis (c). 



Figs 136-147 Outline comparisons of species by overlay technique. Each outline is centred with reference to the junction of the centre of the 
mid-length axis with the centre of the mid-height axis. Outlines are drawn to a similar length. Each shell outline comprises the margin in 
right lateral view, hindgut loop and anterior and posterior adductor muscles. Anterior, posterior ventral and dorsal limits are indicated 
parallel to the relevant shell axis as too is the apex of the umbo. Each limit is identified by the first letters of the species name. The figures 
are in the order of the discussion on the evolution of form. (See text pp. 82-86). 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



85 




lg. 140 Yoldiella artipica (a), Y. similis (s) & (separately) Y. 
lata(p). 




g. 141 Yoldiella sinuosa (s), Y. blanda (bl) & Y. biscayensis (bi). 




Fig. 142 Yoldiella Jeffrey si (j) & Y. enata (en). 




Fig. 143 Yoldiella ella (el). 




Fig. 144 Yoldiella americana (a), Y. subcircularis (s) & Y. perplexa 
(P). 



86 




J. A. ALLEN, H.L. SANDERS AND F. HANNAH 
f 





Fig. 145 Yoldiella ovata (o), Y. biguttata (b) & (separately) Y. 
insculpta (i). 




Fig. 146 Yoldiella fabula (f ) . 




Fig. 147 Portlandia abyssorum (a), P. minuta (m), P. fora (f), 
(separately) Yoldiella velleta (v) & Portlandia lenticula (1). 






DEEP-SEA PROTOBRANCHIA (BIVALVIA) 

robust shells with lunule & escutcheon 
long broad continuous hinge 
large adductors 

P.minuta 

Rfora 

P. lenticula 

R abyssorum 



87 



hind gut thru' 
to left 

Y.curta- 



Y.veletta 

\ ? 



short hinges 

v . /. 

Y.inconspicua 

Y.extensa 

Y.argentinea 




fragile shells without lunule & escutcheon 
separate hinge plates 
moderately large subequal adductors 



Y.fabula 



subrostrate 
long hinges 
small unequal adductors 



V shaped hind guts 




Y.artipica 



^-'? 



Y.bilanta 

Y.hanna 

Y.capensis 



Y.sinuosa 

Y.blanda 

Y.biscayensis 



Y.pseudo 

Y.enata coils 
Y.jeffreysi 

I 
Y.ella 



Y.lucida 
Y.obesa 
Y.similiris 



single 
hind gut loop 



Y. perplex a 



ata Y.similis 

ovate 

loops 



Y.americana 
Y.subcircularis 
Y. biguttata 
Y. ovata 

I 

Y.insculpta 



multiple 
hind gut loops 
& coils 



increasing 
shell height 
&hind gut length 

ig. 148 Diagram to show resemblances in shell form of the deep-sea species of the genus Yoldiella found in the Atlantic, arranged in 
increasing length and complexity of the hindgut and each group of species arranged in increasing depth sequence. 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 



+ + + + 



+ + + + 



+ + + + 



+ + 



+ + + 



+ + 



+ + + + + 



+ + 



+ + + 



a. 
73 
a. 



I|BUJS 



+ + ++ + + + + + + + + + + +++ + 

+ ++ + + + ++ + +++ + + + ++ + 



UBUB/(UI0J3J3H 

icnbaqns 

jouajsod agjrn 

jouajsod iunipaj/\[ 

jouajsod ijcius 



+ + + + + + + + + + + + + + + + + + + + + + + + + 

+ +++ ++++ + + + 

+ + + + + + + 

+ +++ + + + + + + 

+ +++ ++++ +++ + + + + + + + + 



Suot 
uoqs 



+ + +++ ++ + 

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + 



glKT] 

J-ioqs 



+ + + + ++ + + + + + + + + + + + + + + + + + + + 

+ ++++++ + ++ + 



BXJ 
C 



y ^ t sdooj +z 

y t$ -\ sdooi z 

H V 1 doo| i 

y oj s[ioo +z 

~& OJ S]!OD z 

y oj [loo J 
y oj |iod i/ x 
y oj dooj i 



+ + + + + + + + + + + + 



+ + + + + + 



fN 



o\ o 

r- no 

vo — "* 

I I I 

r- — oo ■* 



— — mo — i^-m — ior)moooo-*r~ - *'^it^t^ — N N ^ N io 

— ' — OlNOlClOO«»OOOOnOONO««-" O — O) 00 00 fN t~- 

IIIIIIIJIIIIIIIIIIIIIIIIII 

muinoOMJO- '*tC2t*~)ir)<r\c^tt>r)0\-3- — o \o ^t- >/") oo © — - 



m o r- p- o 
MM oovo ro 
N »O\0OVO 
u~i -* u-i u~> ■* 

* I I I I I 

On P- (N O NO On 
O O NO w~> O v~> 
r- oo c~) oo in 



a 
c 








ea 

T3 










1/) 








S 




CI 


E 
p 


ou 








V) 


c 
u 
e 




OS 


rj 


c-3 
C 


■2 


3 
O 

c 




c/: 

en 
>> 

ea 


_2 

'-3 


■o 
-3 

3 


Gfl 

O 


c 
c 

-C 


H5 


c 

U 

to 

S3 


3 


^0 

C 

u 
ex 
a 
u 


3 

-' 



MCNNNNNNNnn'* 



CO 

c 
o 

II 

• — ca 
. n 



9 2- « 

?■, a. 2? „ x 

-O s i> ts -S 

2 *s 75 Si 



2 u 

c c 
C3 _2 



O c/) 

11 



SiESS's-g-gSl 



e M ^ £ 5 .5 ■§" " S3 .2 
6 .S .« > £..2 S d -S ._:.-• 3 o £ S3 £ S 7J 



a u k 

111 

(/> C3 CO 



D-a.0,0, ^^^^^^^^^^^J-^^^^^S-^-^^^^^^^^^^^.^^ 



-5 5). 
u 

S Z , 



< U i 



DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



89 



is further extended to three loops to the right and two to the 
left with one loop on each side short and anterior to the 
stomach. The latter is a configuration unique among proto- 
branchs. In these relatively large rounded species the liga- 
ment tends to be relatively large and the hinge plates robust 
and elongate. Most of these species extend from the abyssal 
rise across the abyssal plain. 

Comparison of this latter group with Y. similis is of 
interest. While Y. similis species has a double hind gut loop 
its anatomy is similar to Y. artipica. In particular it has small 
palps with a few broad ridges. 

One species of Yoldiella remains to be mentioned. Yoldi- 
ella fabula differs markedly in its shell characters from all 
other species of Yoldiella (and Portlandia) yet in its internal 
morphology it is close to the basic stem group of the genus. 
Thus, while it is elongate with the umbo set far posterior to 
the mid-vertical line, it has relatively short separate hinge 
plates with a small amphidetic ligament. Very large subequal 
adductors are present and the hind gut is a simple, single loop 
to the right. Although its shell outline is unique, these 
characters fit best with the yoldiellids and we are presently 
persuaded to keep it within this subfamily. 

In the foregoing discussion, stress has been placed on 
changes in the shape of the shell and the disposition of the 
gut. It is clear that for the most part species that occur at great 
depths have longer guts than those in shallow water and that 
this increased length has been accommodated within a small 
body space. This in turn relates to the digestive requirement 
to deal with sparse complex organics in deep-sea sediments. 
Indeed, in general the body space of deep-sea bivalves as a 
percentage of shell volume is significantly smaller than that of 
shallow-water congeners. Similarly, in regard to shell shape, 
species in shallower depths appear to be of an elongate-ovate 
shape, whereas those from the deep have higher shells which 
are either more rounded or have the greatest length measure- 
ment dorsal to the mid-horizontal plane. This we believe is 
related to the softness of the abyssal sediments and the ease 
of movement within them. 

There are other evolutionary trends that may or may not be 
depth related. For instance, the size of the adductors clearly 
relates inversely to the strength and length of the hinge plates 
and the size of the ligament. In contrast, the size of the palps 
appears to increase with increasing depth range, while gills 
tend to reduce in size. We believe this is for a different reason 
from that of the change in shape of gut and shell, and relates 
in part to a difference of energy demand at high pressures and 
in part to the lack of importance of the protobranch gill in the 
feeding process. Because of this latter there is a reduction in 
the size of the gill, however, the loss in ciliated tissue is 
compensated by an increase in palp area which is required in 
order to maintain ciliary flow within the mantle cavity. At the 
same time it provides ciliary activity where is is most needed 
in the processing of fine abyssal sediments. 

As might be expected the siphons also show modifications. 
Reduction in the gill area results in lower inhalent siphonal 
flow rates. In contrast, larger palp surfaces result in higher 
inflow via the feeding aperture. The processing of large 
quantities of fine sediment must produce increased numbers 
of faecal pellets. The predicted result from these changes is 
: realized in the increased importance and size of the feeding 
| aperture, the reduction and in some cases elimination of the 
'inhalent siphon or the loss of division between exhalent and 
inhalent siphonal lumena such that the combined siphon is 
largely used for the passage of faecal material to the outside. 



Finally, we speculate that not only that the small size of the 
body in comparison with the shell volume in the deep-water 
species is related to reduced food resources (as in reduced 
numbers of ova) but it is also related to the reduction of 
overall metabolic energy requirements at high pressures. 

Like all protobranchs, the yoldiellids have large eggs and 
larval development is almost certainly short-lasting, non- 
feeding and takes place close to the sea floor. Although there 
are subtle basinal differences in shell form, some of which 
may be sufficiently distinct to establish subspecies (e.g. Y. 
obesa and Y. inconspicua) there is little doubt that either 
widespread gene flow occurs and/or that genetic change is 
slow. Clearly, the yoldiellid form is one that is extremely 
successful. The subfamily contains by far the most species of 
all the protobranch families and subfamilies. 

Much of the scientific discussion on the distribution of the 
Yoldiellinae will be incorporated into a following and final 
round-up paper on the diversity and zoogeography of the 
deep-sea protobranchs of the Atlantic. Nevertheless, because 
it is such a large group, the distribution of the 29 species of 
the genus Yoldiella described here reflect many of the general 
features of protobranch distribution. Thus, of the 29 species 
only a limited number can be regarded as being widespread 
(Table 3). Only six species are present in five or more of the 
Atlantic abyssal basins and of these, five are abyssal and one 
is lower slope/abyssal rise in its depth distribution. There are 
16 endemic species, of these five species and one subspecies 
are restricted to the Argentine Basin. A further four endemic 
species are found in the Cape or Angola Basins. Thus, it is 
clear that most endemic species are in the South Atlantic. 
Furthermore, the South Atlantic has been much less sampled 
than the North and one would suspect that more rare 
endemic species will be reported in the future. This is clearly 
of considerable importance in speculations on the origin of 
the protobranch fauna of the Atlantic. Although endemic 
species are not restricted to upper slope depths, most of the 
species at upper slope depths are endemic and those few that 
are not, are restricted to the North European and North 
American Basins. Thus, in general, the deeper the species 
occurs, the more widespread is likely to be its distribution. 
This may simply reflect the fact that the abyssal plains contain 
enormous areas of sediment of similar characteristics and that 
distribution simply reflects the commonality of the environ- 
ment. 



REFERENCES 



Alien, J.A. 1992. The evolution of the hindgut of the deep-sea protobranch 

bivalves. American Malacological Bulletin, 9: 187-191. 
Allen, J.A. & Hannah, F.J. 1986. A reclassification of the Recent genera of the 

sublass Protobranchia (Mollusca: Bivalvia). Journal of Conchology, 32: 

225-249. 
Allen, J.A. & Hannah F.J. 1989. Studies on the deep-sea Protobranchia. The 

subfamily Ledellinae (Nuculanidae). Bulletin of the British Museum (Natural 

History), Zoology, 55: 123-171. 
Allen, J.A. & Sanders, H.L. 1973. Studies on the deep-sea Protobranchia, the 

families Siliculidae and Lametilidae. Bulletin of the Museum of Comparative 

Zoology Harvard, 145: 263-310. 
Allen, J.A. & Sanders, H.L. 1982. H.L. Studies on the deep-sea Protobranchia. 

The subfamily Spinulinae (family Nuculanidae). Bulletin of the Museum of 

Comparative Zoology Harvard, 150: 1-30. 
Allen, J.A. & Sanders, H.L. The zoogeography and diversity of the deep-sea 

protobranch bivalves of the Atlantic (in m.s). 
Clarke, A.H. Jr. 1963. Arctic archibenthal and abyssal mollusks. Two mollusks 



90 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 



dredged from drifting ice station Charlie (Alpha 2). Bulletin, National 

Museum of Canada, 185: 90-109. 
Jeffreys, J.G. 1876. Preliminary reports of the biological results of a cruise in 

H.M.S. 'Valorous' to Davis Straits in 1875. Proceedings of the Royal Society 

of London, 25:177-237. 
Jeffreys, J.G. 1879. On the Mollusca procured during the 'Lightening' and 

'Porcupine' Expeditions 1868-1870. Part II. Proceedings of the Zoological 

Society of London, 1879: 553-558. 
Knudsen, J. 1970. The symstematics and biology of the abyssal and hadal 

Bivalvia. Galathea Reports, 11: 241. 
Locard, A. 1898. Mollusques Testaces. Expeditions Scientifiques du Travailleur 

etdu Talisman, 2: 1-515. 
Ockelmann, K.W. 1955. The Zoology of East Greenland. Marine Lamellibran- 

chiata. Meddelelser om Grfynland, 122: 1-258. 
Odhner, N.H. 1960. Mollusca. Reports of the Swedish Deep-Sea Expedition 2, 

Zoology, (22): 367-400. 
Rhind, P.M. & Allen, J. A. 1992 Studies on the deep-sea Protobranchia 

(Bivalvia): the family Nuculidae. Bulletin of the British Museum (Natural 

History), Zoology, 58: 61-93. 
Sars, G.O. 1878. Bidrag til kundskaben om Norges artiske Fauna 1, Mollusca 

regionis articae Norvegiae. 466 p. Christiana. 
Sanders, H.L. & Allen, J. A. 1973. Studies on the deep-sea Protobranchia 

(Bivalvia): Prologue and the Pristglomidae. Bulletin of the Museum of 



Comparative Zoology Harvard, 145: 237-261. 
Sanders, H.L. & Allen, J. A. 1977. Studies on the deep-sea Protobranchia 

(Bivalvia): the family Tindariidae and the genus Pseudotindaria. Bulletin of 

the Museum of Comparative Zoology Harvard, 148: 23-59. 
Sanders, H.L. & Allen, J. A. 1985. Studies on the deep-sea Protobranchia 

(Bivalvia): the family Malletiidae. Bulletin of the British Museum (Natural 

History), Zoology, 49: 195-238. 
Shileiko, A. A. 1985. [The genus Yoldiella auct. as a combined group (Bivalvia, 

Protobranchia)]. Transactions, P.P. Shirshov Institute of Oceanology, 120: 

165-175. 
Stasek, C.R. 1965. Feeding and particle-sorting in Yoldia ensifera (Bivalvia: 

Protobranchia), with notes on other nuculanids. Malacologia, 2: 349-366. 
Verril, A.E. & Bush, K.J. 1898. Revision of the deep-water Mollusca of the 

Atlantic coast of North America with descriptions of new genera and species. 

Part 1. Bivalvia. Proceedings of the U.S. National Museum, 20: 775-901. 
Waren, A. 1978. The taxonomy of some North Atlantic species referred to 

Ledella and Yoldiella (Bivalvia). Sarsia, 63: 213-219. 
Waren, A. 1980. Marine Mollusca described by John Gwyn Jeffreys, with the 

location of type material. Conchological Society of Great Britain and Ireland 

Special Publication No. 1: 1-60. 
Waren, A. 1989. Taxonomic comments on some protobranch bivalves from the 

northeastern Atlantic. Sarsia: 223-259. 



Bulletin of The Natural History Museum 
Zoology Series 



Earlier Zoology Bulletins are still in print. The following can be ordered from Intercept (address on inside front cover). Where the complete 
backlist is not shown, this may also be obtained from the same address. 
Volume 51 No. 2 

No. 1 The Hemiuridae (Digenea) of fishes from the north-east 
Atlantic. D. 1. Gibson and R. A. Bray. Pp. 1-125. £30.40 



No. 2 The Zoogonidae (Digenea) of fishes from the north-east 
Atlantic. R.A. Bray and D. 1. Gibson. 1986. Pp. 
127-206. £21.90 



Volume 52 

No. 1 Miscellanea. 

A revision of the genus Pseudovorticelia Foissner & 

Schiffman, 1974 (Ciliophora: Peritrichida). A. Warren. 

The taxonomic status of the genera Pontigulasia, 

Lagenodifflugia and Zivkovicia (Rhizopoda: 

Difflugiidae). C. G. Ogden. 

A revision of the foraminiferal genus Adercotryma 

Loeblich & Tappan, with a description of A. wrighti sp. 

nov. from British waters. P. Bronnimann & J. E. 

Whittaker. 

Hermit crabs associated with the bryozoan Hippoporidra 

in British waters. J. D. D. Bishop. 

The first zoea of three Pachygrapsus and of Cataleptodius 

lloridanus (Gibbes) from Bermuda and Mediterranean 

(Crustacea: Decapoda: Brachyura). R. W. Ingle. 

A classification of the phylum Sipuncula. P. E. Gibbs & 

E. B. Cutler. 

Two new species of Garra (Teleostei: Cyprinidae) from 

the Arabian peninsula. K. E. Banister. 1987. Pp. 

1-70. £10.75 



No. 2 



No. 3 



No. 4 



No. 5 



No. 6 



No. 7 



No. 8 



A revision of the Suctoria (Ciliophora, 
Kinetofragminophora) 5. The Paracinela and 
Corynophyra problem. Dr C. R. Curds. 1987. Pp. 
71-106. £10.75 

Notes on spiders of the family Salticidae. 1. The Genera 
Spartaeus, Mintonia and Taraxella. F. R. Wanless. 1987. 
Pp. 107-137. £10.00 

Mites of the genus Holoparasitus Oudemans, 1936 
(Mesostigmata: Parasitidae) in the British Isles. K. 
Hyatt. 1987. Pp. 139-164. £8.20 

The phylogenetic position of the Yugoslavian cyprinid fish 
genus Aulopyge Heckel, 1841, with an appraisal of the 
genus Barbus Cuvier & Cloquet, 1816 and the subfamily 
Cyprininae. G. J. Howes. 1987. Pp. 165-196. £10.00 

Revision of the genera Acineria, Trimyema and 
Trochiliopsis (Protozoa, Ciliophora). 1987. Pp. 
197-224. 



£8.50 



The baculum in the Vespertilioninae (Chiroptera: 
Vespertilionidae) with a systematic review, a synopsis of 
Pipistrellus and Eptesicus, and the descriptions of a new 
genus and subgenus. J. E. Hill and D. L. Harrison. Pp. 
225-305. £22.60 

Notes on some species of the genus Amathia (Bryozoa, 
Ctenostomata). P. J. Chimonides. 1987. Pp. 
307-358. £14.50 



Volume 53 

No. 1 Puellina (Bryozoa: Cheilostomata: Cribrilinidae) from 

British and adjacent waters. J. D. D. Bishop & B. G. 

Househam. 1987. Pp. 1-63. £17.20 



No. 3 



No. 4 



Miscellanea. 

Notes on Atlantic and other Asteroidea 5. 
Echinasteridae. Ailsa M. Clark. 
Observations on the marine nematode genus Spirina 
Gerlach, 1963 (Desmodoridae: Spiriniinae) with 
descriptions of two new species. J. W. Coles. 
Caleupodes, a new genus of eupodoid mite (Acari: 
Acariformes) showing primary opisthosomal 
segmentation. A. S. Baker. 

The Barbus perince-Barbus neglectus problem and a 
review of certain Nilotic small Barbus species (Teleostei, 
Cypriniformes, Cyprinidae). K. E. Banister. 1987. Pp. 
65-138. £20.55 

The genera of pelmatochromine fishes (Teleostei, 
Cichlidae). A phylogenetic review. P. H. Greenwood. 
1987. £17.20 

Certain Actiniaria (Cnidaria, Anthozoa) from the Red 
Sea and tropical Indo-Pacific Ocean. K. W. England. 
1987. Pp. 205-292. £23.95 



Volume 54 

No. 1 The cranial muscles and ligaments of macrouroid fishes 
(Teleostei: Gadiformes) functional, ecological and 
phylogenetic inferences. G. J. Howes. 1988. Pp. 
1-62. £16.90 

No. 2 A review of the Macrochelidae (Acari: Mesostigmata) of 
the British Isles. K. H. Hyatt & R. M. Emberson. 1988. 
Pp 63-126. £17.20 

No. 3 A revision of Haplocaulus Precht, 1935 (Ciliophora: 

Peritrichida) and its morphological relatives. A. Warren. 
1988. Pp. 127-152. £8.50 

No. 4 Echinoderms of the Rockall Trough and adjacent areas. 
3. Additional records. R. Harvey, J. D. Gage, D. S. M. 
Billett, A. M. Clark, G. L. J. Paterson. 1988. Pp. 
153-198. £14.00 

No. 5 A morphological atlas of the avian uropygial gland. D. W. 
Johnston. 1988. £16.60 

No. 6 Miscellanea. 

A review of the Copepod endoparasites of brittle stars 

(Ophiuroida). G. A. Boxshall. 

A new genus of tantulocaridan (Crustacea: 

Tantulocarida) parasitic on a harpacticoid copepod from 

Tasmania. G. A. Boxshall. 

Unusual ascothoracid nauplii from the Red Sea. G. A. 

Boxshall & R. Bottger-Schnack. 

New nicothoid copepods (Copepoda: 

Siphonostomatoida) from an amphipod and from deep 

sea isopods. G. A. Boxshall & K. Harrison. 

A new genus of Lichomolgidae (Copepoda: 

Poecilostomatoida) associated with a phoronid in Hong 

Kong. G. A. Boxshall & A. G. Humes. 1988. £9.00 

Volume 55 

No. 1 Miscellanea. 

Structure and taxonomy of the genus Delosina Wiesner, 
1931 (Protozoa: Foraminiferida). S. A. Revets. 
Morphology and morphogenesis of Parakahliella haideri 



No. 2 



nov. spec. (Ciliophora, Hypotrichida). H. Berger & W. 

Foissner. 

Morphology and biometry of some soil hypotrichs 

(Protozoa, Ciliophora) from Europe and Japan. H. 

Berger & W. Foissner. 

Polyclad turbellarians recorded from African waters. S. 

Prudhoe, O.B.E. 

Ten new taxa of chiropteran myobiids of the genus 

Pteracarus (Acarina: Myobiidae). K. Uchikawa. 

Anatomy and phytogeny of the cyprinid fish genus 

Onychostoma Giinther, 1896. C. Yiyu. 1989. Pp. 

1-121. £30.00 

Studies on the Deep Sea Protobranchia: The Subfamily 
Ledellinae (Nuculanidae). J. A. Allen & F. J. Hannah. 
1989. £38.00 



Volume 56 

No. 1 Osteology of the Soay sheep. J. Clutton-Brock, K. 
Dennis-Bryan, P. L. Armitage & P. A. Jewell. 
A new marine species of Euplotes (Ciliophora, 
Hypotrichida) from Antarctica. A. Valbonesi & P. 
Luporini. 

Revision of the genus Eizalia Gerlach, 1957 (Nematoda: 
Xyalidae) including three new species from an oil 
producing zone in the Gulf of Mexico, with a discussion 
of the sibling species problem. D. Castillo-Fernandez & 
P. J. D. Lambshead. 

Records of NebaHa (Crustacea: Lepostraca) from the 
Southern Hemisphere a critical review. Erik Dahl. 
1990. £31.00 

No. 2 Tinogullmia riemanni sp. nov. (Allogromiina: 

Foraminiferida), a new species associated with organic 

detritus in the deep-sea. A. J. Gooday. 

Larval and post-larval development of Anapagurus 

chiroacanthus (Lilljeborg, 1855) Anomura: Paguroidea: 

Paguridae. R. W. Ingle. 

Redescription of Martialia hyadesi Rochebrune and 

Mabille, 1889 (Mollusca: Cephalopoda) from the 

Southern Ocean. P. G. Rodhouse & J. Yeatman. 

The phylogenetic relationships of salmonoid fishes. C. P. 

J. Sanford. 

A review of the Bathygadidae (Teleostei: Gadiformes). 

G. J. Howes & O. A. Crimmen. 1990. £36.00 



Volume 57 

No. 1 Morphology and biometry of twelve soil testate amoebae 
(Protozoa, Rhizopoda) from Australia, Africa and 
Austria. G. Liiftenegger & W. Foissner 
A revision of Cothurnia (Ciliophora: Peritrichida) and its 
morphological relatives. A. Warren & J. Paynter 
Indian Ocean echinoderms collected during the Sinbad 
Voyage (1980-81): 2. Asteroidea. L. M. Marsh & A. R. 
G. Price 

The identity and taxonomic status of Tilapia arnoldi 
Bilchrist and Thompson, 1917 (Teleostei, Cichlidae). P. 
H. Greenwood 

Anatomy, phylogeny and taxonomy of the gadoid fish 
genus Macruronus Giinther, 1873, with a revised 
hypothesis of gadoid phylogeny. G. J. Howes £38.50 

No. 2 The pharyngobranchial organ of mugilid fishes; its 

structure, variability, ontogeny, possible function and 

taxonomic utility. I. J. Harrison & G. J. Howes 

Cranial anatomy and phylogeny of the South-East Asian 

catfish genus Belodontichthys. G. J. Howes & A. 

Fumihito 

A collection of seasnakes from Thailand with new 

records of Hydrophis belcheri (Gray). C. J. McCarthy & 

D. A. Warrell 

The copepod inhabitants of sponges and algae from 

Hong Kong. S. Malt 

The freshwater cyclopoid of Nigeria, with an illustrated 

key to all species. G. A. Boxshall & E. I. Braide 



A new species of Ferdina (Echinodermata: Asteroidea) 
from the Sultanate of Oman with discussion of the 
relationships of the genus within the family 
Ophidiasteridae. L. M. Marsh & A. C. Campbell £38.50 

Volume 58 

No. 1 The morphology and phylogeny of the Cerastinae 
(Pulmonata: Pupilloidea). P. B. Mordan 
A redescription of the uniquely polychromatic African 
cichlid fish Tilapia guinasana Trewavas, 1936. P. H. 
Greenwood 

A revision and redescription of the monotypic cichlid 
genus Pharyngochromis (Teleostei, Labroidei). P. H. 
Greenwood 

Description of a new species of Microgale (Insectivora: 
Tenrecidae) from eastern Madagascar. P. D. Jenkins 
Studies on the deep-sea Protobranchia (Bivalvia): the 
family Nuculidae. P. M. Rhind and J. A. Allen £40.30 

No. 2 Notes on the anatomy and classification of ophidiiform 
fishes with particular reference to the abyssal genus 
Acanthonus Giinther, 1878. G. J. Howes 
Morphology and morphogenesis of the soil ciliate 
Bakuella edaphoni nov. spec, and revision of the genus 
Bakuella Agamaliev & Alekperov, 1976 (Ciliophora, 
Hypotrichida). W. Song, N. Wilbert and H. Berger 
A new genus and species of freshwater crab from 
Cameroon, West Africa (Crustacea, Brachyura, 
Potamoidea, Potamonautidae). N. Cumberlidge and P. 
F. Clark 

On the discovery of the male of Mormonilla Giesbrecht, 
1891 (Copepoda: Mormonilloida) R. Huys, G. A. 
Boxshall and R. Bottger-Schnack £40.30 

Volume 59 

No. 1 A new snake from St Lucia, West Indies. G. Underwood 
Anatomy of the Melanonidae (Teleostei: Gadiformes), 
with comments on its phylogenetic relationships. G. J. 
Howes 

A review of the serranochromine cichlid fish genera 
Pharyngochromis, Sargochromis, Serranochromis and 
Chetia (Teleostei: Labroidei). P. H. Greenwood 
A revision of Danielssenia Boeck and Psammis Sars with 
the establishment of two new genera Archisenia and 
Bathypsammis (Harpacticoida: Paranannopidae). R. 
Huys and J. M. Gee. 

A new species of Syrticola Willems & Claeys, 1982 
(Copepoda: Harpacticoida) from Japan with notes on the 
type species. R. Huys and S. Ohtsuka 
Erratum £40.30 

No. 2 The status of the Persian Gulf sea snake Hydrophis 

lapemoides (Gray, 1849) (Serpentes, Hydrophiidae). A. 

Redsted Rasmussen. 

Taxonomic revision of some Recent agglutinated 

foraminifera from the Malay Archipelago, in the Millett 

Collection, The Natural History Museum, London. P. 

Bronnimann and J. E. Whittaker. 

Foregut anatomy, feeding mechanisms, relationships and 

classification of the Conoidea 

(=Toxoglossa)(Gastropoda). J. D. Taylor, Y. I. Kantor 

and A.V. Sysoev. 1993. Pp. 97-170. £40.30 

Volume 60 

No. 1 A new subfamily and genus in Achatinidae (Pulmonata: 
Sigmurethra). A. R. Mead. 

On Recent species of Spiraserpula Regenhardt, 1961, a 
serpulid polychaete genus hitherto known only from 
Cretaceous and Tertiary fossils. T. Gottfried Pillai and 
H.A. Ten Hove. 1994. Pp. 1-104. £40.30 

No. 2 Phylogenetic relationships between arietellid genera 

(Copepoda: Calanoida), with the establishment of three J 
new genera. S. Ohtsuka, G. A. Boxshall and H. S. J. 
Roe. 1994. Pp. 105-172. £40.30 






GUIDE FOR AUTHORS 



Policy. The Bulletin of the British Museum (Natural His- 
tory) Zoology, was established specifically to accommodate 
manuscripts relevant to the Collections in the Department of 
Zoology. It provides an outlet for the publication of taxo- 
nomic papers which, because of their length, prove difficult 
to publish elsewhere. Preference is given to original contribu- 
tions in English whose contents are based on the Collections, 
or the description of specimens which are being donated to 
enhance them. Acceptance of manuscripts is at the discretion 
of the Editor, on the understanding that they have not been 
submitted or published elsewhere and become the copyright 
of the Trustees of the Natural History Museum. All submis- 
sions will be reviewed by at least two referees. 

Manuscripts. Initially three clear, complete copies should 
be submitted in the style and format of the Bulletin. The text 
must be typed double-spaced throughout, including refer- 
ences, tables and legends to figures, on one side of A4 paper 
with 2.5 cm margins. All pages should be numbered consecu- 
tively, beginning with the title page as p. 1. SI units should be 
I used where appropriate. 

Whenever possible a copy of the text, once the paper has 
been accepted, should also be provided on floppy disc (see 
below). Discs should only be sent after final acceptance, as 
papers generally need revision after refereeing. If it is impos- 
sible to provide an appropriate disc please ensure that the 
final typescript is clearly printed. 

Authors are requested to ensure that their manuscripts are 
in final format, because corrections at proof stage may be 
charged to the author. Additions at proof stage will not 
normally be allowed. Page proofs only will be sent. 



Word-processor discs. Please follow these instructions. 

1. Ensure that the disc you send contains only the final 
version of the paper and is identical to the typescript. 

2. Label the disc with the author's name, title of the 
paper and the word-processor programme used. Indicate 
whether IBM or Apple Mac (IBM preferred). 

3. Supply the file in the word-processor format; if there 
is a facility to save in ASCII please submit the file in ASCII as 
well. 

4. Specify any unusual non-keyboard characters on the 
front page of the hard copy. 

5. Do not right-justify the text. 

6. Do not set a left-hand margin. 

7. Make sure you distinguish numerals from letters, 
e.g. zero (0) from O; one (1) from 1 (el) and I. 

8. Distinguish hyphen, en rule (longer than a hyphen, 
used without a space at each end to signify 'and' or 'to', e.g. 
the Harrison-Nelson technique, 91-95%, and increasingly 
used with a space at each end parenthetically), and em rule 
(longer than an en rule, used with a space at each end 
parenthetically) by: hyphen, two hyphens and three hyphens, 
respectively. Be consistent with rule used parenthetically. 

9. Use two carriage returns to indicate beginnings of 
paragraphs. 

10. Be consistent with the presentation of each grade of 
heading (see Text below). 

Title. The title page should be arranged with the full title; 
name(s) of author(s) without academic titles; institutional 
address(es); suggested running title; address for correspon- 
dence. 

Synopsis. Each paper should have an abstract not exceeding 
200 words. This should summarise the main results and conclu- 



sions of the study, together with such other information to make 
it suitable for publication in abstracting journals without change. 
References must not be included in the abstract. 

Text. All papers should have an Introduction, Acknowledge- 
ments (where applicable) and References; Materials and Meth- 
ods should be included unless inappropriate. Other major 
headings are left to the author's discretion and the requirements 
of the paper, subject to the Editors' approval. Three levels of 
text headings and sub-headings should be followed. All should 
be ranged left and be in upper and lower case. Supra-generic 
systematic headings only should be in capitals; generic and 
specific names are to be in italics, underlined. Authorities for 
species names should be cited only in the first instance. Foot- 
notes should be avoided if at all possible. 

References. References should be listed alphabetically. 
Authorities for species names should not be included under 
References, unless clarification is relevant. The author's 
name, in bold and lower case except for the initial letter, 
should immediately be followed by the date after a single 
space. Where an author is listed more than once, the second 
and subsequent entries should be denoted by a long dash. 
These entries should be in date order. Joint authorship 
papers follow the entries for the first author and an '&' should 
be used instead of 'and' to connect joint authors. Journal 
titles should be entered in full. Examples: (i) Journals: 
England, K.W. 1987. Certain Actinaria (Cnidaria, Antho- 
zoa) from the Red Sea and tropical Indo-Pacific Ocean. 
Bulletin of the British Museum (Natural History), Zoology 53: 
206-292. (ii) Books: Jeon, K.W. 1973. The Biology of 
Amoeba. 628 p. Academic Press, New York & London, (iii) 
Articles from books: Hartman, W.D. 1981. Form and distri- 
bution of silica in sponges, pp. 453-493. In: Simpson, T.L. & 
Volcani, B.E. (eds) Silicon and Siliceous Structures in Bio- 
logical Systems. Springer- Verlag, New York. 

Tables. Each table should be typed on a separate sheet 
designed to extend across a single or double column width of a 
Journal page. It should have a brief specific title, be self- 
explanatory and be supplementary to the text. Limited space in 
the Journal means that only modest listing of primary data may 
be accepted. Lengthy material, such as non-essential locality 
lists, tables of measurements or details of mathematical deriva- 
tions should be deposited in the Biological Data Collection of 
the Department of Library Services, The Natural History 
Museum, and reference should be made to them in the text. 

Illustrations. Figures should be designed to go across single 
(84 mm wide) or double (174 mm wide) column width of the 
Journal page, type area 235 x 174 mm. Drawings should be 
in black on white stiff card or tracing film with a line weight 
and lettering suitable for the same reduction throughout, 
either 50%, 30% or 25%. After reduction the smallest 
lettering should be not less than 10 pt (3 mm). All photo- 
graphs should be prepared to the final size of reproduction, 
mounted upon stiff card and labelled with press-on lettering. 
Components of figure-plates should be abutted. All figures 
should be numbered consecutively as a single series. Leg- 
ends, brief and precise, must indicate scale and explain 
symbols and letters. 

Reprints. 25 reprints will be provided free of charge per 
paper. Orders for additional reprints can be submitted to the 
publisher on the form provided with the proofs. Later orders 
cannot be accepted. 



CONTENTS 

1 A revised familial classification for certain cirrhitoid genera (Teleostei, Percoidei 
Cirrhitoidea), with comments on the group's monophyly and taxonomic ranking 
P.H. Greenwood 
11 Studies on the deep-sea Protobranchia (Bivalvia); the Subfamily Yoldiellinae 

J. A. Allen, H.L Sanders and F. Hannah 




ZOOLOGY SERIES 

Vol. 61, No. 1, June 1995